Optical products, masters for fabricating optical products, and methods for manufacturing masters and optical products

ABSTRACT

An optical product can be configured, when illuminated, to reproduce an image that appears to be a 3D image of at least a part of a 3D object. The optical product can include a surface comprising a plurality of portions. Each portion can correspond to a point on a surface of the 3D object. One or more non-holographic features can be disposed within each portion configured to produce at least part of the image without relying on diffraction. An interference optical structure can be disposed on one or more features. A gradient in the features can correlate to a surface normal of the surface of the 3D object at the corresponding point. An orientation of the features can correlate to an orientation of the surface of the 3D object at the corresponding point.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of priority to U.S. ProvisionalApplication No. 63/088,937, entitled “OPTICAL PRODUCTS, MASTERS FORFABRICATING OPTICAL PRODUCTS, AND METHODS FOR MANUFACTURING MASTERS ANDOPTICAL PRODUCTS,” filed Oct. 7, 2020. The entirety of each applicationreferenced in this paragraph is incorporated herein by reference.

TECHNICAL FIELD

The present application generally relates to optical products, masters(e.g., master and/or daughter shims) for fabricating an optical product,and methods for manufacturing the masters and optical products. Inparticular, the optical products can be configured, when illuminated, toreproduce by reflected and/or transmitted (or refracted) light, a 3Dimage (e.g., an image that appears three-dimensional) of at least a partof a 3D object. The optical products can include one or morenon-holographic features with thin interference structures, films,coatings, and pigments potentially configured to produce color in bothreflection mode and transmission mode. These structures, films,coatings, and pigments can possibly exhibit color shifting propertieswith changes in reflection and/or transmission with a change in theangle of incidence or the viewing angle.

DESCRIPTION OF THE RELATED TECHNOLOGY

Optical products can be used for a variety of purposes such as toreproduce a 3D image. Such products can be placed on decorative signs,labels, packaging, and consumer goods. Counterfeiting continues at ahigh level and poses risks. Given the level of counterfeiting, an easyidentifiable image on a tag or on the actual item is desirable for thepublic at large so individuals can tell if they are receiving a genuinearticle or a fake one. Accordingly, some optical products can be used asan anti-counterfeit feature, for example, on goods (e.g., handbags,watches, clothing, cosmetics, pharmaceuticals, etc.) or on currency(e.g., a banknote). Holograms have traditionally been used as acounterfeit deterrent. However, this technology has become so widespreadwith hundreds if not thousands of holographic shops around the worldthat holograms are now viewed as having poor security. Opticallyvariable inks and optically variable magnetic inks have also enjoyed forthe past decade a high security place on banknotes. However, theseproducts have now been simulated or have been even made from similarmaterials as the originals that these security elements are now beingquestioned as a high security feature. Motion type security elementshave been adopted into banknotes, but even here, security has beencompromised as this feature has also been used on commercial products.Thus, what is needed is a new security feature that the average personreadily recognizes, has no resemblance to holograms or inks, is readilyverified as to its authenticity, is difficult to counterfeit, is easilymanufactured in quantity and can be readily incorporated into an itemsuch as packaging, a tag, a consumer product, or a banknote.

Color shifting features can be used to prevent counterfeiting. The colorshifting effect produced by color shifting materials can be easy for thecommon person to observe. The color shifting effect produced by thecolor shifting features, however, can be impractical to recreate usingcounterfeit copies produced by color copiers, printers and/orphotographic equipment. Color copiers, printers and/or photographicequipment use pigments based on dyes having absorption and as such theprinted colors can be insensitive to a change in the viewing angle.Therefore, the difference between an authentic item comprising colorshifting features and a fake one can be detected by tilting the item toobserve if there is a color shift. Some color shifting features that areavailable are opaque and exhibit a color shift for reflection mode.Additionally, counterfeiters have developed sophisticated methods thatcompromise the effectiveness of the existing reflective color shiftingfeatures as counterfeit protection. Thus, a new anti-counterfeit opticalproduct that is difficult to counterfeit and can be readily incorporatedinto an item such as packaging, a tag, a consumer product, or a banknoteis desirable.

Manufacturing such optical products, e.g., in relatively largequantities for commercial use, can utilize a master to fabricate theoptical product. A master can be either a negative or positive master.For example, a negative master can form a surface of the optical productthat is complementary to the surface of the master. As another example,a positive master can provide a surface for the optical product that issubstantially similar to the surface of the master.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A schematically illustrates an example master and optical productin accordance with certain embodiments described herein.

FIG. 1B schematically illustrates a top view of the surface of a masterfor fabricating an optical product in accordance with certainembodiments described herein.

FIG. 1C schematically illustrates the inclination and orientation of asurface of a 3D object at a point on the surface.

FIG. 1D is another example optical product 10′ in accordance withcertain embodiments described herein.

FIG. 1E is another example optical product 10′ in accordance withcertain embodiments described herein.

FIG. 2 illustrates an example method to manufacture a master forfabricating an optical product in accordance with certain embodimentsdescribed herein.

FIG. 2A illustrates an example method that can be used to manufacture asurface relief diffuser.

FIGS. 2B-2C illustrate example methods to manufacture a master forfabricating an optical product in accordance with certain embodimentsdescribed herein.

FIGS. 3A-3B illustrate example 2D data files in accordance with certainembodiments disclosed herein.

FIGS. 3C-3D illustrate example features on a data file and thecorresponding features on the surface of a master for fabricating anoptical product in accordance with certain embodiments disclosed herein.

FIG. 4A illustrates another example 2D data file in accordance withcertain embodiments disclosed herein.

FIG. 4B illustrates an example normal map used to generate the data fileshown in FIG. 4A.

FIG. 4C illustrates the 3D image reproduced by an optical productgenerated from a master produced using the data file shown in FIG. 4A.

FIG. 5 schematically illustrates a cross-sectional view of an exampleoptical product with an interference optical structure disposed onnon-holographic features.

FIG. 6 schematically illustrates an example optical product producingcolored depth perception in an image.

FIG. 7A shows an example planar view of a reproduced object andbackground.

FIG. 7B shows another example planar view of a reproduced object andbackground.

FIG. 8 shows another example planar view of a reproduced object andbackground.

FIG. 9 shows another example planar view of a reproduced object andbackground.

FIG. 10 shows another example view of a reproduced object andbackground.

FIG. 11 schematically illustrates a side view of an optical structureconfigured to be used as a security feature.

FIGS. 12A-1 and 12A-2 schematically illustrate side views of opticalstructures configured to be used as a security feature in the form of aplatelet encapsulated with an encapsulating layer, comprising, forexample, a SiO₂ layer and silica spheres.

FIGS. 12B-1 and 12B-2 illustrates a plurality of platelets dispersed ina polymer which can comprise an ink or a paint medium.

FIG. 13 illustrates the silane coupling agent bonded to an exposedsurface of the encapsulation layer of a platelet. Another side of thesilane coupling agent can also bond to a medium such as a polymer inwhich the platelets are dispersed.

FIG. 14 is a schematic illustration showing propagation light incidenton the optical structure and the resultant nodes in field strength atthe metal layers.

FIGS. 15A and 15B illustrate transmission and reflection spectra ofexamples of optical structures.

FIGS. 16A-16D and 17A-17D are a* b* plots showing the color travel orchange in reflection and transmission respectively for four differentexample optical structures.

FIGS. 18A and 18B respectively illustrate the transmittance andreflectance spectra for an example of the optical structure.

FIGS. 18C and 18D respectively illustrate the transmittance andreflectance spectrum for an example of the optical structure.

FIGS. 18E and 18F respectively illustrate the transmittance andreflectance spectrum for an example of the optical structure.

FIG. 18G illustrates the a*b* values in the CIE L*a*b* color space foran example of the optical structure for different viewing angles between0 degrees and 40 degrees with respect to the normal to the surface ofthe example of the optical structure in transmission mode.

FIG. 18H illustrates the a*b* values in the CIE L*a*b* color space foran example of the optical structure for different viewing angles between0 degrees and 40 degrees with respect to the normal to the surface ofthe example of the optical structure in reflection mode.

FIG. 19A schematically illustrates a cross-sectional view of anembodiment of an optical structure configured to be used as a securityfeature. FIG. 19B schematically illustrates a cross-sectional view ofanother embodiment of an optical structure configured to be used as asecurity feature.

FIG. 20 is a schematic illustration of a laminate structure comprisingan optical structure that is affixed to a banknote.

FIG. 21A shows a banknote with two windows, each window including adifferent optical structure. FIG. 21B shows a security device with twoat least partially overlapping windows, each window comprising adifferent optical structure.

FIGS. 22 and 23 illustrate examples of a security device comprising anoptical structure disposed under or over a text, symbol or number. Thetext, symbol or number becomes visible when the viewing angle ischanged.

FIG. 24A schematically illustrates a side view of an implementation ofan optical structure comprising a stack of layers that can be used as asecurity feature.

FIG. 24B illustrates a cross-sectional view of an implementation of anoptical structure including a first region comprising a first metallicmaterial which is surrounded by a second region comprising a dielectricmaterial which in turn is surrounded by a third region comprising asecond metallic material.

FIG. 25A is a CIE 1931 color space chromaticity diagram showing the xand y chromaticity coordinates of light transmitted through a firstexample of the optical structure shown in FIG. 24A or 24B for differentviewing angles between 0 degrees and 40 degrees with respect to a normalto a surface of the optical structure.

FIG. 25B is a CIE 1931 color space chromaticity diagram showing the xand y chromaticity coordinates of light reflected from the first exampleof the optical structure shown in FIG. 24A or 24B for different viewingangles between 0 degrees and 40 degrees with respect to a normal to asurface of the optical structure.

FIG. 25C illustrates the a*b* values in the CIE L*a*b* color space whenthe first example of the optical structure shown in FIG. 24A or 24B isviewed in the transmission mode at different viewing angles between 0degrees and 40 degrees with respect to the normal to the surface of thefirst example of the optical structure.

FIG. 25D illustrates the a*b* values in the CIE L*a*b* color space whenthe first example shown in FIG. 24A or 24B of the optical structure isviewed in the reflection mode at different viewing angles between 0degrees and 40 degrees with respect to the normal to the surface of thefirst example of the optical structure.

FIG. 26A is a CIE 1931 color space chromaticity diagram showing the xand y chromaticity coordinates of light transmitted through a secondexample of the optical structure shown in FIG. 24A or 24B for differentviewing angles between 0 degrees and 40 degrees with respect to a normalto a surface of the optical structure.

FIG. 26B is a CIE 1931 color space chromaticity diagram showing the xand y chromaticity coordinates of light reflected from the secondexample of the optical structure shown in FIG. 24A or 24B for differentviewing angles between 0 degrees and 40 degrees with respect to a normalto a surface of the optical structure.

FIG. 26C illustrates the a*b* values in the CIE L*a*b* color space whenthe second example of the optical structure shown in FIG. 14A or 14B isviewed in the transmission mode at different viewing angles between 0degrees and 40 degrees with respect to the normal to the surface of thesecond example of the optical structure.

FIG. 26D illustrates the a*b* values in the CIE L*a*b* color space whenthe second example of the optical structure shown in FIG. 24A or 24B isviewed in the reflection mode at different viewing angles between 0degrees and 40 degrees with respect to the normal to the surface of thesecond example of the optical structure.

FIG. 27A shows the variation of the transmittance with wavelength for athird example of the optical structure shown in FIG. 24A or 24B at aviewing angle of about 0 degrees with respect to a normal to the surfaceof the optical structure 300 a/300 b.

FIG. 27B shows the variation of the reflectance with wavelength for thethird example of the optical structure shown in FIG. 24A or 24B at aviewing angle of about 0 degrees with respect to a normal to the surfaceof the optical structure.

FIG. 27C is a CIE 1931 color space chromaticity diagram showing the xand y chromaticity coordinates of light transmitted through the thirdexample of the optical structure shown in FIG. 24A or 24B for differentviewing angles between 0 degrees and 40 degrees with respect to a normalto a surface of the optical structure.

FIG. 27D illustrates the a*b* values in the CIE L*a*b* color space whenthe third example of the optical structure shown in FIG. 24A or 24B isviewed in the transmission mode at different viewing angles between 0degrees and 40 degrees with respect to the normal to the surface of thethird example of the optical structure.

FIG. 27E is a CIE 1931 color space chromaticity diagram showing the xand y chromaticity coordinates of light reflected from the third exampleof the optical structure shown in FIG. 24A or 24B for different viewingangles between 0 degrees and 40 degrees with respect to a normal to asurface of the optical structure.

FIG. 27F illustrates the a*b* values in the CIE L*a*b* color space whenthe third example of the optical structure shown in FIG. 24A or 24B isviewed in the reflection mode at different viewing angles between 0degrees and 40 degrees with respect to the normal to the surface of thethird example of the optical structure.

FIG. 28A shows the variation of the transmittance with wavelength for afourth example of the optical structure shown in FIG. 24A or 24B at aviewing angle of about 0 degrees with respect to a normal to the surfaceof the optical structure.

FIG. 28B shows the variation of the reflectance with wavelength for thefourth example of the optical structure shown in FIG. 24A or 24B at aviewing angle of about 0 degrees with respect to a normal to the surfaceof the optical structure.

FIG. 28C is a CIE 1931 color space chromaticity diagram showing the xand y chromaticity coordinates of light transmitted through the fourthexample of the optical structure for different viewing angles between 0degrees and 40 degrees with respect to a normal to a surface of theoptical structure.

FIG. 28D illustrates the a*b* values in the CIE L*a*b* color space whenthe fourth example of the optical structure shown in FIG. 24A or 24B isviewed in the transmission mode at different viewing angles between 0degrees and 40 degrees with respect to the normal to the surface of thefourth example of the optical structure.

FIG. 28E is a CIE 1931 color space chromaticity diagram showing the xand y chromaticity coordinates of light reflected from the fourthexample of the optical structure shown in FIG. 24A or 24B for differentviewing angles between 0 degrees and 40 degrees with respect to a normalto a surface of the optical structure.

FIG. 28F illustrates the a*b* values in the CIE L*a*b* color space whenthe fourth example of the optical structure is viewed in the reflectionmode at different viewing angles between 0 degrees and 40 degrees withrespect to the normal to the surface of the fourth example of theoptical structure 300 a/300 b.

FIG. 29A shows the variation of the transmittance, reflectance andabsorptance with wavelength for a fifth example of the optical structureshown in FIG. 24A or 24B at a viewing angle of about 0 degrees withrespect to a normal to the surface of the optical structure.

FIG. 29B is a CIE 1931 color space chromaticity diagram showing the xand y chromaticity coordinates of light transmitted through the fifthexample of the optical structure shown in FIG. 24A or 24B for differentviewing angles between 0 degrees and 40 degrees with respect to a normalto a surface of the optical structure.

FIG. 29C illustrates the a*b* values in the CIE L*a*b* color space whenthe fifth example of the optical structure shown in FIG. 24A or 24B isviewed in the transmission mode at different viewing angles between 0degrees and 40 degrees with respect to the normal to the surface of thefifth example of the optical structure.

FIG. 29D is a CIE 1931 color space chromaticity diagram showing the xand y chromaticity coordinates of light reflected from the fifth exampleof the optical structure shown in FIG. 24A or 24B for different viewingangles between 0 degrees and 40 degrees with respect to a normal to asurface of the optical structure.

FIG. 29E illustrates the a*b* values in the CIE L*a*b* color space whenthe fifth example of the optical structure shown in FIG. 24A or 24B isviewed in the reflection mode at different viewing angles between 0degrees and 40 degrees with respect to the normal to the surface of thefifth example of the optical structure.

FIGS. 30A and 30B are CIE 1931 color space chromaticity diagramsrespectively showing the x and y chromaticity coordinates of lighttransmitted through and reflected from various implementations of anoptical structure having a geometry similar to the geometry of theimplementations illustrated in FIGS. 24A and 24B.

FIGS. 31A and 31B respectively illustrate the transmittance andreflectance spectra for example optical structures with and withoutprotective layers.

DETAILED DESCRIPTION

In various embodiments, a master (e.g., a master and/or daughter shim)for fabricating an optical product is provided. The optical product,when illuminated, can reproduce an overt 3D image (e.g., an image thatappears 3D to the naked eye) of a 3D object. Compared to ink printedimages, the reflective surface of various embodiments of the opticalproduct can produce a brighter mirror-like image produced by reflecting(or refracting) light incident on the surface. In certain suchembodiments, the surface normals of the 3D object are mimicked assurface relief on the master and/or optical product. The surface reliefon the master and/or optical product can be thinner than the 3D object,yet produce the same appearance of the 3D object. This property issimilar to Fresnel lenses, where the surface relief allows a lens to beproduced that is thinner than a comparable non-Fresnel lens. UnlikeFresnel lenses, however, certain embodiments disclosed herein are notlimited in the type of 3D object that can be reproduced (e.g., linearand regularly shaped objects). As such, realistic and bright 3D imagescan be produced on relatively thin films (e.g., 300 μm and less inthickness, 250 μm and less in thickness, 200 μm and less in thickness,150 μm and less in thickness, 100 μm and less in thickness, 75 μm andless in thickness, 50 μm and less in thickness, 30 μm and less inthickness, 25 μm and less in thickness, 15 μm and less in thickness, orany ranges in between these values or any ranges formed by thesevalues). In various implementations, the optical product can compriseone or more thin films. Thin films may be advantageous for differentapplications. In addition, special effects can be integrated into theimage. In various embodiments described herein, the optical product canadvantageously be used in applications for flexible packaging, brandidentification, tamper evident containers, currency (e.g., a banknote),decoding messages, authenticity, and security, etc. Some securityapplications include incorporation of small detailed features,incorporation of non-symmetrical features, incorporation of machinereadable features, etc.

In certain embodiments, the optical product can be incorporated into anitem as an embedded feature, a laminated feature, a hot stamp feature, awindowed thread feature, or a transparent window feature. For example,on an item such as a banknote, the optical product can be a patch, awindow, or a thread. The optical product can have a thickness of lessthan 350 μm, less than 300 μm, less than 250 μm, less than 200 μm, lessthan 150 μm, less than 100 μm, less than 75 μm, less than 50 μm, lessthan 30 μm, less than 25 μm, or less than 15 m or any ranges in betweenthese values or any ranges formed by these values. In variousembodiments, the image can appear 3D by the naked eye.

In some embodiments, the image can be seen at a viewing angle between 20degrees to 160 degrees, between 15 degrees to 165 degrees, between 10degrees to 170 degrees, between 5 degrees to 175 degrees, or between 0degrees to 180 degrees relative to the plane of the item (e.g., relativeto the banknote plane) as the item is tilted. For example, the image canbe viewable within one or more of these viewing angle ranges relative tothe plane of the item.

In some embodiments, the image can be seen at a viewing angle between 20degrees to 90 degrees, between 15 degrees to 90 degrees, between 10degrees to 90 degrees, between 5 degrees to 90 degrees, or between 0degrees to 90 degrees relative to the normal of the item as the item isrotated the normal of the item (e.g., in the plane of the item). Forexample, the image can be viewable and/or visible within one or more ofthese viewing angle ranges as the item is rotated (e.g., rotated atleast throughout the range of 90 degrees, rotated at least throughoutthe range of 180 degrees, rotated at least throughout the range of 270degrees, or rotated at least throughout the range of 360 degrees) aboutthe normal of the item (e.g., in the plane of the item).

FIG. 1A schematically illustrates an example master 10 for fabricatingan optical product 10′ in accordance with certain embodiments describedherein. In various embodiments, the master 10 can include a firstsurface 11 and a second surface 12 opposite the first surface 11. Asshown in FIG. 1A, the second surface 12 can include a plurality ofportions P₁, P₂, . . . P_(n). Each portion P₁ can correspond to aplurality of portions P′₁, P′₂, . . . P′_(n) on the optical product 10′.The plurality of portions P′₁, P′₂, . . . P′_(n) on the optical product10′ can also be referred to as a cell, pixel, or a tile. Each portionP′_(n) can have a length between 1 μm and 100 μm, between 7 μm and 100μm, or any range within these ranges (e.g., between 20 μm and 100 μm,between 7 μm and 50 μm, between 7 μm and 35 μm, between 10 μm and 55 μm,between 12.5 μm and 100 μm, between 12.5 μm and 50 μm, between 12.5 μmand 35 μm, between 20 μm and 50 μm, between 35 μm and 55 μm, between 40μm and 50 μm, etc.). Each portion P′_(n) can have a width between 1 μmand 100 μm, between 7 μm and 100 μm, or any range within these ranges(e.g., between 20 μm and 100 μm, between 7 μm and 50 μm, between 7 μmand 35 μm, between 10 μm and 55 μm, between 20 μm and 50 μm, between12.5 μm and 100 μm, between 12.5 μm and 50 μm, between 12.5 μm and 35μm, between 35 μm and 55 μm, between 40 μm and 50 μm, etc.).Accordingly, in various embodiments, the aspect ratio of each portionP′_(n) can be 1:1 or 1:1.1.

Each portion P₁₁ of the master 10 (and each portion P′_(n) of theoptical product 10′) can correspond to a point S₁, S₂, . . . S_(n) on asurface S of the 3D object 50. Each portion P₁ can include features F₁,F₂, . . . F_(n) corresponding to elements E₁, E₂, . . . E_(n), e.g.,non-holographic elements, on the optical product 10′. A gradient (e.g.,slope) in the features F₁, F₂, . . . F_(n) can correlate to aninclination (e.g., slope) of the surface S of the 3D object 50 at thecorresponding point S₁, S₂, . . . S_(n). For example, in variousimplementations, for individual ones of the portions, a gradient of thefeatures can correlate to an inclination of the surface of the 3D objectat the corresponding point. In addition, an orientation of the featuresF₁, F₂, . . . F_(n) can correlate to an orientation of the surface S ofthe 3D object 50 at the corresponding point S₁, S₂, . . . S_(n). Forexample, in various implementations, for individual ones of theportions, an orientation of the features can correlate to an orientationof the surface of the 3D object at the corresponding point. Accordingly,with certain embodiments disclosed herein, an optical product 10′fabricated using the example master 10 can be configured, whenilluminated, to reproduce by reflected (or refracted) light, a 3D image50′ (e.g., an image that appears 3D) of at least a part of a 3D object50. The image can be observed by the naked eye and under variouslighting conditions (e.g., specular, diffuse, and/or low lightconditions).

In various implementations, the features on the master and/or opticalproduct can be different than the 3D object, yet produce the sameappearance of the 3D object. In addition, certain implementationsdisclosed herein are not limited in the type of 3D object that can bereproduced (e.g., an irregularly shaped object, a regularly shapedobject, a non-symmetrical shaped object, a symmetrical shaped object, anobject in nature, a man-made object, etc.). In various optical products,the features (e.g., non-holographic elements) can reproduce at leastpart of the 3D image without use of lenses. In some implementations, asdescribed herein, lenses can be used to improve contrast and/orsharpness of the image.

The optical product 10′ can be used on a variety of products toreproduce a 3D image 50′ of at least a part of a 3D object 50. Forexample, the optical product 10′ can be placed on decorative signs,advertisements, labels (e.g., self-adhesive labels), packaging (e.g.,consumer paper board packaging and/or flexible packaging), consumergoods, collectible cards (e.g., baseball cards), etc. The opticalproduct 10′ can also be advantageously used for authenticity andsecurity applications. For example, the optical product 10′ can beplaced on currency (e.g., a banknote), credit cards, debit cards, stockcertificates, passports, driver's licenses, identification cards,documents, tamper evident containers and packaging, consumer packaging,bottles of pharmaceuticals, etc.

In various implementations, the optical product 10′ can be a reflectiveor transmissive device. For example, the optical product 10′ can includereflective material (e.g., reflective metal such as aluminum, copper, orsilver disposed on the plurality of elements E₁, E₂, . . . E_(n), or atransparent, relatively high refractive index material such as ZnS orTiO₂ disposed on the plurality of elements E₁, E₂, . . . E_(n) creatinga semi-transmitting/partially reflective boundary). In some instances,the relatively high refractive index material can have a refractiveindex from 1.65 to 3.0. In some instances, the relatively highrefractive index material can have a refractive index from 1.8 to 3.0.Depending on the thickness of the reflective material, the opticalproduct 10′ can be reflective or transmissive. Depending on thethickness of the reflective material, the optical product 10′ can bepartially reflective or partially transmissive. The thickness of thereflective material at which the optical product 10′ is reflective ortransmissive can depend on the chemical composition of the reflectivematerial.

Accordingly, in some embodiments, the optical product 10′ can include areflective surface 12′ from which light can reflect from the elementsE₁, E₂, . . . E_(n) to reproduce the image 50′ of the 3D object 50 or atleast part of the 3D object 50. For example, the optical product 10′ canbe made of a reflective metal (e.g., aluminum, copper, or silver), asemi-transparent metal, or a material (e.g., polymer, ceramic, or glass)coated with a reflective metal. Reflective coatings that employnon-metallic material can also be employed.

In some embodiments where the elements E₁, E₂, . . . E_(n) are coatedwith a reflective metal, the thickness of the coating layer can begreater than or equal to 40 nm such that the layer is opaque.Alternatively, the thickness of the reflective metal can be less than 40nm such that the layer is semi-transparent (e.g., 30% transparent 40%transparent, 50% transparent, 60% transparent, 70% transparent, or anyranges formed by any of these values, etc.). In reflective embodiments,the elements E₁, E₂, . . . E_(n) can reflect light towards or away fromthe observer's eye to reproduce the image 50′ the 3D object 50. Forexample, the elements E₁, E₂, . . . E_(n) can reflect light towards theobserver's eye in bright areas, and reflect light away from theobserver's eye in dark areas. In some embodiments, the slopes of theelements E_(n) can be configured to create the 3D depth perception ofthe image. For example, elements E_(n) with less steep slopes can causelight to reflect toward the observer's eye creating more brightness,while elements E_(n) with steeper slopes can cause light to reflect awayfrom the observer's eye creating more darkness.

In some other embodiments (e.g., for a transmissive device), the opticalproduct 10′ can include a layer (e.g., a coating) of a transparent,relatively high refractive index material such as, for example, ZnS orTiO₂. In some such embodiments, light can transmit through the materialand can also reflect at each of the elements E₁, E₂, . . . E_(n) due tothe presence of the relatively high index layer which can create indexmismatch and results in Fresnel reflection. The relatively high indexmaterial can be up to a full visible wavelength in thickness in someembodiments. If a color tint is used, the relatively high index materialcan be up to a ¼ of a visible wavelength in thickness in someembodiments.

Furthermore, the optical product 10′ can include a protective covering,e.g., an organic resin, to protect the elements E₁, E₂, . . . E_(n)and/or any coating layer from corrosion from acidic or basic solutionsor organic solvents such as gasoline and ethyl acetate or butyl acetate.In various implementations, the protective covering can also provideprotection during subsequent processing steps and use of the opticalproduct 10′ (e.g., during the manufacturing of currency and/or bygeneral handling by the public).

In various embodiments, the optical product 10′ can be placed on or inanother surface (e.g., as an embedded feature, a hot stamped featuresuch as a patch, a windowed thread feature, or a transparent windowfeature). In other embodiments, the optical product 10′ can be placedunder another surface (e.g., a laminated feature laminated under a filmand/or cast cured). In some embodiments, the optical product 10′ can beplaced between two other surfaces (e.g., hot stamped on another surfaceand laminated under a film). Additional features associated with theoptical product 10′ will become apparent with the disclosure herein ofthe master 10 for fabricating the optical product 10′.

The image 50′ of at least part of the 3D object 50 can be reproducedwhen the optical product 10′ is illuminated. In various embodiments, theimage 50′ can be reproduced by a multitude of relatively small mirrors(e.g., each of the elements E₁, E₂, . . . E_(n) having both a length andwidth between 30 μm and 100 μm, between 35 μm and 55 μm, or between 40μm and 50 μm) which can be curved (e.g., have a freeform curvature) orplanar. For example, in some embodiments, a reflective surface of theoptical product 10′ can provide a surface for specular reflection, suchthat the image 50′ can be produced by the reflected light (e.g., like amirror). Accordingly, various embodiments can produce a bright, highquality image. Some embodiments can also utilize techniques forproducing diffuse reflection, e.g., for special or desired effects.Furthermore, the image 50′ can be a substantially similar reproduction(e.g., with similar details), an approximate reproduction (e.g., withless details), a not scaled copy (e.g., not scaled up or down in size),and/or a scaled copy (e.g., scaled up or down in size) of the 3D object50 or part of the 3D object 50.

In general, the 3D object 50 to be reproduced is not particularlylimited and can advantageously include rotationally non-symmetricaland/or irregularly shaped objects, as well as symmetrical and/orregularly shaped objects. For example, the 3D object 50 can include oneor more alphanumeric characters and/or symbols. For example, the 3Dobject 50 can include one or more text, one or more alphabeticcharacters, one or more numeric characters, one or more letters, one ormore numbers, one or more symbols, one or more punctuation marks, one ormore mathematical operators, etc. The 3D object 50 can also include oneor more graphical images or logos, e.g., a company logo, a team logo,product branding designs, etc. Accordingly, the 3D object 50 can includeirregularly shaped features in addition to planar and curved features.In some embodiments, the 3D object 50 can comprise animals, humans,plants or trees, landscapes, buildings, cars, boats, airplanes,bicycles, furniture, office equipment, sports equipment, foods, drinks,personal care items, flags, emblems, symbols like country, company orproduct symbols including trademarks, or parts thereof or groups orcombination of these items with or without other items. The objects maybe cartoon or artistic renditions. A wide range of other objects arepossible. In some implementations, the produced image can be a QuickResponse or QR code.

As set forth herein, in various embodiments, the image 50′ can be seenat various viewing angles (e.g., between 20 degrees to 160 degrees,between 15 degrees to 165 degrees, between 10 degrees to 170 degrees,between 5 degrees to 175 degrees, or between 0 degrees to 180 degreesrelative to the plane of the item (e.g., relative to the banknoteplane). For example, when the example optical product 10′ is tilted,upon viewing the example optical product 10′ at different viewing angles(or upon different angles of illumination), different sets of elementsE₁, E₂, . . . E_(n) can be seen by the observer to provide the differentimages of the 3D object.

In some embodiments, the image can be seen at a viewing angle between 20degrees to 90 degrees, between 15 degrees to 90 degrees, between 10degrees to 90 degrees, between 5 degrees to 90 degrees, or between 0degrees to 90 degrees relative to the normal of the item as the item isrotated about the normal of the item. For example, the image can beviewable within one or more of these viewing angle ranges as the item isrotated (e.g., rotated at least throughout the range of 90 degrees,rotated at least throughout the range of 180 degrees, rotated at leastthroughout the range of 270 degrees, or rotated at least throughout therange of 360 degrees) about the normal of the item.

Furthermore, in certain embodiments, the image 50′ can be substantiallywithout iridescence or change in color with angle. For example, invarious embodiments, there are substantially no colors (e.g., rainboweffect), other diffractive colors, or ghosting effects in the image 50′.For example, in certain embodiments, the size of the portions P′₁, P′₂,. . . P′_(n) can have a length and width between 1 μm and 200 μm,between 7 μm and 200 μm, or any range within these ranges (e.g., between20 μm and 100 μm, between 7 μm and 50 μm, between 7 μm and 35 μm,between 10 μm and 55 μm, between 12.5 μm and 100 μm, between 12.5 μm and50 μm, between 12.5 μm and 35 μm, between 20 μm and 50 μm, between 35 μmand 55 μm, between 40 μm and 50 μm, between about 65 μm and 80 μm,between about 50 μm and 100 μm, between about 60 μm and 90 μm, betweenabout 100 μm and 200 μm, etc.). In some such embodiments (e.g., between20 μm and 50 μm), the portions P′_(n) may be small enough such that theportions P′₁ are not resolvable by a human observer under normal viewingconditions (e.g., a reading distance of 18 to 24 inches between the eyeand the item to be viewed). In addition, without being bound by theory,the portions P′_(n) may be big enough such that the cone of lightpassing through the pupil (e.g., 5 mm in diameter) is small enough suchthat the eye may see a majority of the colors mixed as white light at adistance of 18-24 inches.

As another example, in some embodiments, a majority (e.g., greater than50%, greater than 55%, greater than 60%, greater than 65%, greater than70%, greater than 80%, greater than 90%, and any ranges in between thesevalues) of the plurality of portions P′₁, P′₂, . . . P′_(n) on theoptical product 10′ can include a single non-holographic element E₁ (asopposed to a plurality of spaced apart non-holographic elements E_(n)that may resemble a grating-like feature). Without being bound bytheory, grating-like features can cause light to be dispersed with someof the light collected by the pupil of the eye. If the period of thegrating-like feature is small enough, the light captured by the pupilmay appear as a color. Accordingly, in various embodiments of theoptical product 10′ that have a majority of the plurality of portionsP′₁, P′₂, . . . P′_(n) having not more than a single non-holographicreflective or refractive element E₁, unwanted color caused bygrating-like features may possibly be substantially reduced and/oreliminated. Similarly, color change with angle of tilt can be reduced.In some embodiments, at least 20%, at least 30%, at least 40%, at least50%, at least 60%, at least 70%, at least 80%, at least 90%, or anyranges in between these values) of the plurality of portions P′₁, P′₂, .. . P′_(n) on the optical product 10′ can include a singlenon-holographic element E₁. In various embodiments, the single elementmay be slowly varying and/or substantially flat. In certain embodiments,the maximum average slope per portion with a single feature is less than½, less than ⅓, less than ¼, less than ⅕, less than ⅙, potentially flat,and any ranges in between these values depending on feature height andwidth.

In addition, in portions P′_(n) having a plurality of non-holographicelements E₁, E₂, . . . E_(n)(e.g., grating-like features), the elementsE_(n) can be discontinuous and/or having different orientation withnon-holographic elements E₁, E₂, . . . E_(n) in surrounding adjacentportions P′_(n). Without being bound by theory, the discontinuity and/ordifferent orientations between grating-like features can cause a lateralshift of the grating-like feature. The lateral shift may cause the colorspectrum to shift as well (e.g., from red to blue to green). The colorsmay combine on the retina providing an average white irradiancedistribution. Accordingly, in embodiments of the optical product 10′that have a plurality of portions P′₁, P′₂, . . . P′_(n) including aplurality of non-holographic element E_(n), unwanted color cause bygrating-like features may possibly be substantially reduced and/oreliminated. Similarly, color change with angle of tilt can be reduced.

In some implementations, a majority of the portions can comprisenon-holographic features with discontinuities. In some instances, amajority of portions can comprise features discontinuous with featuresin surrounding adjacent portions. In some instances, a majority offeatures can be discontinuous at boundaries between adjacent portions.

Accordingly, certain embodiments of the optical product 10′ can utilizea certain portion P′_(n) size, a single non-holographic element E₁ in aportion P′_(n), discontinuous and/or differently orientated elementsE_(n) to produce images that may be substantially without iridescence orchange in color with angle. The application of these features can bedependent on the image to be formed.

Various embodiments described herein can create a 3D image primarily bythe reflection of light without relying on diffraction (e.g., withoutrelying on holographic or grating diffraction). In other embodiments,the optical product 10′ can include surfaces which additionally includefeatures from which light can diffract, e.g., at surface defects, atdiscontinuities at borders, and/or via incorporation of diffractive orholographic elements. Such diffractive or holographic features can becombined with the surface features disclosed herein that produce animage of a 3D object using reflection (or possibly refraction, e.g., intransmission) without relying on diffraction.

In various embodiments, the master 10 can be either a negative orpositive master. Whether as a negative or positive master, the method toproduce the master 10 is not particularly limited. For example, thefeatures F₁, F₂, . . . F_(n) on surface 12 of the master 10 can beproduced using any technique known in the art or yet to be developed,including but not limited to photolithography (e.g., UV or visiblelight), electron beam lithography, and ion beam lithography to name afew. Additionally, the materials that can be used to manufacture themaster 10 are not particularly limited and can include glasses,ceramics, polymers, metals, etc.

As a negative master, the master 10 can form a surface 12′ of theoptical product 10′ that is complementary to the surface 12 of themaster 10. For example, as shown in FIG. 1A, the features F₁, F₂, . . .F_(n) on the surface 12 of the master 10 can be the inverse of theelements E₁, E₂, . . . E_(n) on the surface 12′ of the optical product10′. In such embodiments, the master 10 can be used to form the opticalproduct 10′. For example, the master 10 can be used to emboss theelements E₁, E₂, . . . E_(n) onto a metal sheet, a polymeric substratesuch as a thermoformable polymer, or a UV curable photoresist layer suchas a UV curable resin, or to injection mold the elements E₁, E₂, . . .E_(n) onto a polymer.

As another example, as a positive master, the master 10 can provide asurface 12′ for the optical product 10′ that is substantially similar tothe surface 12 of the master 10. The features F₁, F₂, . . . F_(n) on thesurface 12 of the master 10 can be substantially similar to the elementsE₁, E₂, . . . E_(n) on the surface 12′ of the optical product 10′. Insome such embodiments, the positive master 10 can provide a model forthe optical product 10′. In other such embodiments, the positive master10 can be used to create an inverse image of the 3D object 50. Inaddition, the positive master 10 can be used to fabricate one or morenegative masters.

Although the master 10 is shown producing a product directly, in certainembodiments the master 10 is employed to produce one or more othermasters (e.g., daughter shims) or intermediate surfaces that can in turnbe used to produce a product. For example a first negative master can beused to produce a second master that is a positive master. The secondpositive master can be used to make a third negative master. The thirdnegative master can be used to produce a fourth positive master. Thefourth positive master can be used to produce a product. Accordingly, atooling tree of masters (e.g., four, five, six, etc. generations deep)can be produced.

Certain embodiments of the optical product 10′ disclosed herein can beadvantageously manufactured on a large industrial scale. Someembodiments can be manufactured by embossing the elements E₁, E₂, . . .E_(n) into an UltraViolet (UV) curable resin coated onto variouspolymeric substrates, such as, for example, polyethylene terephthalate(PET), oriented polypropylene (OPP), biaxially oriented polypropylene(BOPP), low density polyethylene (LDPE), linear low density polyethylene(LLDPE), polypropylene (PP), polyvinyl chloride (PVC) polycarbonate (PC)or any other type of plastic film or carrier. For thermoformableplastics such as PVC and PC, the elements E₁, E₂, . . . E_(n) can beembossed directly into the substrate without the UV curable layer. Invarious embodiments, the polymeric substrate can be clear. The polymericsubstrates can have a thickness less than or equal to 300 microns (e.g.,less than or equal to 250 microns, less than or equal to 200 microns,less than or equal to 150 microns, less than or equal to 100 microns,less than or equal to 50 microns, less than or equal to 25 microns, lessthan or equal to 15 microns, etc.). Some such polymeric substrateshaving elements E₁, E₂, . . . E_(n) can be formed into security threadsthat can be incorporated into a banknote having a paper or polymerthickness of 100 microns, 150 microns, or any thickness up to 300microns. Other thicknesses are also possible.

With continued reference to FIG. 1A, the master 10 can include a firstsurface 11 and a second surface 12. The first surface 11 is shown forsimplicity as a planar surface. However, the shape of the first surface11 is not particularly limited. The second surface 12 can be oppositethe first surface 11. In various implementations, the second surface canbe planar. However, the shape of the second surface in not particularlylimited. The second surface 12 can include a plurality of portions P₁,P₂, . . . P_(n). In some embodiments, the plurality of portions P₁, P₂,. . . P_(n) can form a single cell (e.g., a mono-cell). In otherembodiments, the plurality of portions P₁, P₂, . . . P_(n) can form aplurality of cells. For example, each of the plurality of portions P₁,P₂, . . . P_(n) can form a cell of the plurality of cells. The number ofcells is not particularly limited and can depend on factors such as sizeand resolution of the image to be reproduced. In various embodiments,the portions P₁, P₂, . . . P_(n) can form a pixelated surface. Forsimplicity, only one row of portions P₁, P₂, . . . P_(n) is shown inFIG. 1A. However, certain embodiments can include additional rows andcolumns of portions P₁, P₂, . . . P_(n). For example, as shown in FIG.1B, the portions P₁, P₂, . . . P_(n) can include a plurality of rows andcolumns spanning across the surface 12 of the master 10. For simplicity,only the first row is labeled as P₁, P₂, . . . P_(n). Furthermore,although FIG. 1B shows a 4×4 array of portions P₁, P₂, . . . P_(n), thenumbers of rows, columns, and portions P₁, P₂, . . . P_(n) are notparticularly limited. In some instances, the portions can form at leasta 4×4 array of rows and columns. In some instances, the portions cancomprise from 10 to 20 portions. In some instances, the portions cancomprise more than 20 portions (e.g., up to 50 portions, up to 100portions, up to 200 portions, up to 300 portions, up to 400 portions, upto 500 portions, etc. or any ranges formed by any of these values).

As also shown in FIG. 1B, in some embodiments, borders 13 can surroundat least part of the portions P₁, P₂, . . . P_(n). The borders 13 cansubstantially surround a portion P_(n), or can surround just part of aportion P_(n). In some embodiments, discontinuities can extend aroundall or substantially all of the portion P_(n). In other embodiments,discontinuities may extend on just a part of the portion P_(n). Invarious implementations, the portions can be defined by the borders. Theborders 13 can help define the size and shape of the portions P₁, P₂, .. . P_(n) in some embodiments. However, the size and shape of theportions P₁, P₂, . . . P_(n) are not particularly limited. For example,some of the portions P₁, P₂, . . . P_(n) can comprise a symmetricalshape. For example, the symmetrical shape can include a rectangle, asquare, a rhombus, an equilateral triangle, an isosceles triangle, aregular polygon (e.g., a regular pentagon, a regular hexagon, a regularoctagon, etc.), to name a few. In various instances, the portions can bedefined by linear borders. The symmetrical shape can also includecurvature, e.g., a circle, an ellipse, etc. In other embodiments, someof the portions P₁, P₂, . . . P_(n) can comprise a non-symmetricalshape, e.g., a non-rotationally symmetrical shape, and/or an irregularshape. In some embodiments, some of the portions P₁, P₂, . . . P_(n) canhave a shape that is substantially the same as other portions P₁, P₂, .. . P_(n). In some embodiments, at least 20%, at least 30%, at least40%, at least 50%, at least 60%, at least 70%, at least 80%, at least90% (or any range in between these percentages) of the portions P₁, P₂,. . . P_(n) can have the same shape, size, or both. In otherembodiments, some of the portions P₁, P₂, . . . P_(n) can have a shapethat is different from other portions P₁, P₂, . . . P_(n).

Arrangement of the portions P₁, P₂, . . . P_(n) is not particularlylimited. For example, whether with or without borders, whethersymmetrically shaped or non-symmetrically shaped, or whether regularlyor irregularly shaped, the portions P₁, P₂, . . . P_(n) can form aperiodic array. In other embodiments, whether with or without borders,whether symmetrically shaped or non-symmetrically shaped, or whetherregularly or irregularly shaped, the portions P₁, P₂, . . . P_(n) canform an aperiodic array. In yet other embodiments, the portions P₁, P₂,. . . P_(n) can form a combination of periodic and aperiodic arrays.

With continued reference to FIG. 1A, each portion P₁ can correspond to apoint S₁, S₂, . . . S_(n) on the surface S of the 3D object 50, and eachportion P₁ can include one or more features F₁, F₂, . . . F_(n). Forsimplicity, the features F₁, F₂, . . . F_(n) shown in FIG. 1A appearlinear and substantially similar to each other. However, the featuresF₁, F₂, . . . F_(n) can vary in number, size, shape, and orientation.

In certain embodiments, the features F₁, F₂, . . . F_(n) can includelinear and/or curved features, for example as seen from a top or frontview. In some embodiments, the features F₁, F₂, . . . F_(n) can includefacets, such as linear or curved saw tooth shaped features. The size ofthe features F₁, F₂, . . . F_(n) are not particularly limited. However,from a manufacturing and economic perspective, in some embodiments, asmaller height (e.g., 0 μm to 10 μm) can be advantageous to reduce theamount of material used. Accordingly, in some embodiments, the heightsof the features F₁, F₂, . . . F_(n) can be from close to 0 μm to 0.1 μm(e.g., 0 nm to 100 nm, 1 nm to 75 nm, or 1 nm to 50 nm), from close to 0μm to 1 μm (e.g., 0 nm to 1000 nm, or 1 nm to 500 nm), from close to 0μm to 5 μm (e.g., 1 nm to 5 μm, 10 nm to 5 μm, 50 nm to 5 μm, 75 nm to 5μm, 0.1 μm to 5 μm, 0.5 μm to 5 μm, or 1 μm to 5 μm), or from close to 0μm to 8 μm (e.g., nm to 8 μm, 10 nm to 8 μm, 50 nm to 8 μm, 75 nm to 8μm, 0.1 μm to 8 μm, 0.5 μm to 8 μm, or 1 μm to 8 μm), or from close to 0μm to 10 μm (e.g., 1 nm to 10 μm, 10 nm to 10 μm, 50 nm to 10 μm, 75 nmto 10 μm, 0.1 μm to 10 μm, 0.5 μm to 10 μm, or 1 μm to 10 μm). In otherembodiments, the heights of the features F₁, F₂, . . . F_(n) can go upto 15 μm, up to 20 μm, up to 25 μm, or any ranges from 1 μm, 2 μm, or 3μm up to 25 μm. In yet other embodiments, the heights of the featuresF₁, F₂, . . . F_(n) can go up to 50 μm if needed, e.g., depending on thedesired size of the 3D image to be reproduced.

Furthermore, in some embodiments, the lateral dimensions of the featuresF₁, F₂, . . . F_(n) are not particularly limited, but can depend on thedetails of the 3D object. For example, for text, the lateral dimensionsof the features F₁, F₂, . . . F_(n) can be less than 1 μm. Accordingly,the lateral dimensions of the features F₁, F₂, . . . F_(n) can be fromclose to 0 μm to 0.1 μm (e.g., 0 nm to 100 nm, 1 nm to 75 nm, or 1 nm to50 nm), from close to 0 μm to 1 μm (e.g., 0 nm to 1000 nm, or 1 nm to500 nm), from close to 0 μm to 5 μm (e.g., 1 nm to 5 μm, 10 nm to 5 μm,50 nm to 5 μm, 75 nm to 5 μm, 0.1 μm to 5 μm, 0.5 μm to 5 μm, or 1 μm to5 μm), or from close to 0 μm to 8 μm (e.g., 1 nm to 8 μm, 10 nm to 8 μm,50 nm to 8 μm, 75 nm to 8 μm, 0.1 μm to 8 μm, 0.5 μm to 8 μm, or 1 μm to8 μm), or from close to 0 μm to 10 μm (e.g., 1 nm to 10 μm, 10 nm to 10μm, 50 nm to 10 μm, 75 nm to 10 μm, 0.1 μm to 10 μm, 0.5 μm to 10 μm, or1 μm to 10 μm).

In various embodiments, a lateral distance between two features can bedefined in some embodiments as a pitch. In some embodiments, the pitchbetween features within a portion P₁ can be substantially the samewithin the portion P_(n). For example, in various embodiments, inportion P₁ of the portions P₁, P₂, . . . P_(n), the feature F₁ cancomprise a plurality of features that form a periodic array such thatthe pitch is substantially the same within portion P₁. In addition, insome embodiments, the features F₁, F₂, . . . F_(n) among the multipleportions P₁, P₂, . . . P_(n), can form a periodic array such that thepitch is substantially the same among the portions P₁, P₂, . . . P_(n).In other embodiments, the features could be chirped and form anaperiodic array such that the pitch may be different among multipleportions P₁, P₂, . . . P_(n). However, although the pitch may bedifferent for different portions P₁, P₂, . . . P_(n), the pitch can beslowly varying (e.g., less than 15% change per lateral distance, lessthan 12% change per lateral distance, less than 10% change per lateraldistance, less than 8% change per lateral distance, less than 5% changeper lateral distance, less than 3% change per lateral distance, or lessthan 1% change per lateral distance) among the portions P₁, P₂, . . .P_(n). In some embodiments, the pitch may uniformly change acrossmultiple portions P₁, P₂, . . . P_(n). In other embodiments, thefeatures could be chirped within a portion P₁ such that the pitch may bedifferent within the portion P₁. In some such embodiments, the pitchwithin the portion P_(n) may slowly vary (e.g., less than 15% change perlateral distance, less than 12% change per lateral distance, less than10% change per lateral distance, less than 8% change per lateraldistance, less than 5% change per lateral distance, less than 3% changeper lateral distance, or less than 1% change per lateral distance). Insome embodiments, the pitch may uniformly change with the portion P_(n).The pitch in certain embodiments can be between 1 μm and 100 μm, between1 μm and 75 μm, between 1 μm and 50 μm, or between 1 μm and 25 μm.

With continued reference to FIG. 1A, the features F₁, F₂, . . . F_(n)can correspond to elements E₁, E₂, . . . E_(n) on the optical product10′, and since the optical product 10′ is configured to reproduce the 3Dobject 50, aspects of the features F₁, F₂, . . . F_(n) can correlate toaspects of the surface S of the 3D object 50 at the corresponding pointS₁, S₂, . . . S_(n). For example, a gradient (e.g., slope) in thefeatures F₁, F₂, . . . F_(n) can correlate to an inclination of thesurface S of the 3D object 50 at the corresponding point S₁, S₂, . . .S_(n). For example, in various embodiments, each feature can include aslope. A slope of the feature F₁ can correlate to the inclination of thesurface S of the 3D object 50 at the corresponding point S₁. As shown inFIG. 1C, the slope of the feature F₁ can correlate to the polar angle θ₁from reference line R₁ of the 3D object 50. Accordingly, the slopes ofthe features F₁, F₂, . . . F_(n) can mimic the surface normals of the 3Dobject 50.

Various embodiments can advantageously have a uniform gradient (e.g.,uniform slope) within each portion P₁ such that the gradient is a singlevalue (e.g., a single polar angle θ_(n)) at the corresponding pointS_(n) on the surface S of the 3D object 50. In other embodiments, thefeature F_(n) within a portion P_(n) includes a plurality of features,and the features within the portion P_(n) may have more than onegradient (e.g., different slopes). In such embodiments, the averagegradient (e.g., average slope) of the features within the portion P_(n)can correlate to the inclination of the surface S of the 3D object 50 atthe corresponding point S_(n).

In some embodiments, varying the slopes within and/or among portions P₁,P₂, . . . P_(n) can create contrast on the surface and therefore, on theimage 50′. Furthermore, varying at least one of the height of features,pitch between features (e.g., lateral distance between two features),and slope of the features in one or more portions P₁, P₂, . . . P_(n)can be used in authenticity and security applications. For example, onecan intentionally vary the pitch within one or more portions P_(n), butmaintain the given slopes. The image 50′ of the 3D object 50 would bereproduced, yet upon closer inspection of the presence of theintentional variation within one or more portions P₁, P₂, . . . P_(n),authenticity can be verified. Other variations are possible.

In various embodiments, the orientation of features F₁, F₂, . . . F_(n)can correlate to an orientation of the surface S of the 3D object 50 atthe corresponding point S₁, S₂, . . . S_(n). For example, an orientationof the feature F₁ can correlate to the orientation of the surface S ofthe 3D object 50 at the corresponding point S₁. As shown in FIG. 1C, theorientation of the feature F₁ can correlate to the azimuth angle φ₁ fromreference line R₂ of the 3D object 50. Various embodiments canadvantageously have a uniform orientation within each portion P_(n),such that the orientation is a single value (e.g., a single azimuthangle φ_(n)) at the corresponding point S_(n) on the surface S of the 3Dobject 50. In other embodiments, the feature F_(n) within a portionP_(n) includes a plurality of features, and the features within theportion P₁ may have more than one orientation (e.g., differentorientations). In such embodiments, the average orientation of thefeatures within the portion P_(n) can correlate to the orientation ofthe surface S of the 3D object 50 at the corresponding point S_(n).Furthermore, the orientation of the features within and among theportions P₁, P₂, . . . P_(n), can slowly vary (e.g., less than 15%change per lateral distance, less than 12% change per lateral distance,less than 10% change per lateral distance, less than 8% change perlateral distance, less than 5% change per lateral distance, less than 3%change per lateral distance, or less than 1% change per lateraldistance) within and among the portions P₁, P₂, . . . P_(n).

In some embodiments, where a feature F₁ includes multiple featureswithin a portion, the features can appear discontinuous with otherfeatures within the portion. In some embodiments where the surface 12 ofthe master 10 is pixelated (e.g., having a plurality of cells), thefeatures F₁, F₂, . . . F_(n) can appear discontinuous with features insurrounding adjacent portions. In other embodiments, the portions P₁,P₂, . . . P_(n) can form a single cell or a mono-cell. In some suchembodiments, the features F₁, F₂, . . . F_(n) can appear continuous andsmoothly varying depending on the shape. In other such embodiments, thefeatures F₁, F₂, . . . F_(n) can appear discontinuous due todiscontinuities in the 3D object 50.

In some instances, the features F₁, F₂, . . . F_(n) can comprise one ormore linear and/or non-linear features when viewed in a cross-sectionorthogonal to the first and second surfaces. In some embodiments, thefeatures F₁, F₂, . . . F_(n) can comprise linear features correspondingto a substantially smooth region of the surface S of the 3D object 50.The features F₁, F₂, . . . F_(n) can also comprise non-linear features,e.g., curved features as seen from a top or front view, corresponding toa curved region of the surface S of the 3D object 50, e.g., instead offlat facets. In some embodiments, features F₁, F₂, . . . F_(n) that arelinear can be used to correspond to a curved region of the surface S ofthe 3D object 50. In some such embodiments, linear features on a master10 can be used to represent a curved region by using a piecewiseapproximation function (e.g., a piecewise linear function such as afunction comprising straight line sections). In some other embodiments,features F₁, F₂, . . . F_(n) that are non-linear can be used tocorrespond to a substantially smooth region of the surface S of the 3Dobject 50. In some such embodiments, non-linear features on a master 10can be used to represent smooth regions on the surface S of the 3Dobject because the features F₁, F₂, . . . F_(n) can correspond torelatively small sized features on the optical product 10′. For example,the pitch and/or texture on the optical product 10′ can be between 1 μmand 100 μm, between about 1 μm and about 75 μm, between about 1 μm andabout 50 μm, or between about 1 μm and about 25 μm.

With continued reference to FIG. 1A, as described herein, the featuresF₁, F₂, . . . F_(n) can correspond to aspects of the surface S of the 3Dobject 50 and can also correspond to elements E₁, E₂, . . . E_(n) on theoptical product 10′ such that the optical product 10′ can reproduce animage 50′ of the 3D object 50. In various embodiments, the elements E₁,E₂, . . . E_(n) on the optical product 10′ can be non-holographic. Forexample, the elements E₁, E₂, . . . E_(n) do not need to rely onholography (e.g., effects based on diffraction and/or based on opticalinterference) to render a 3D image 50′ of the 3D object 50. In some suchembodiments, the features F₁, F₂, . . . F_(n) on the surface 12 of themaster 10 can include non-sinusoidal features or non-quasi-sinusoidalfeatures. In general, sinusoidal or quasi-sinusoidal features can bediffractive with +/− orders of equal intensity that generate a twinimage. One positive order and one negative order can share the incidentlight and result in a simultaneous twin image with counter-intuitivemovement of one image with respect to the other. Such effects may benon-ideal. In some embodiments that include non-sinusoidal ornon-quasi-sinusoidal features, the features F₁, F₂, . . . F_(n) on thesurface 12 of the master 10 can include other shapes, such as sawtoothed shapes as described herein.

Although various embodiments described herein do not necessarily rely onholography to reproduce an image, some embodiments can includediffractive or holographic features (e.g., less than about 50% of thesurface area, less than about 40% of the surface area, less than about30% of the surface area, less than about 20% of the surface area, lessthan about 10% of the surface area, less than about 5% of the surfacearea, less than about 3% of the surface area, less than about 2% of thesurface area, or less than about 1% of the surface area) to be used inconjunction with the non-holographic elements E₁, E₂, . . . E_(n)described herein. For example, in some embodiments, the second surface12 of the master 10 can further comprise features corresponding toholographic elements on the optical product 10′ in one or more portionsP₁, P₂, . . . P_(n). In other embodiments, a holographic layer can beadded over or under the surface 12′ of the optical product 10′.

FIG. 1D is another example optical product 10′ in accordance withcertain embodiments described herein. As shown in FIG. 1D, the opticalproduct 10′ can include a plurality of portions P′₁, P′₂, . . . P′_(n).Each portion P′_(n) can include elements E₁, E₂, . . . E_(n), e.g.,non-holographic elements, on the optical product 10′. In some suchembodiments, the elements E₁, E₂, . . . E_(n) can be embossed on thebottom surface of the substrate, e.g. UV curable resin having arefractive index of 1.5. The elements E₁, E₂, . . . E_(n) can be coatedwith a reflective coating. The elements E₁, E₂, . . . E_(n) may then beembedded between the substrate and the item to which the optical product10′ is attached. As described herein, the slopes of the elements E₁, E₂,. . . E_(n) can be configured to create the 3D depth perception of theimage. For example, elements E₁, E₂, . . . E_(n) with less steep slopescan cause light to reflect toward the observer's eye creating morebrightness, while elements E₁, E₂, . . . E_(n) with steeper slopes cancause light to reflect away from the observer's eye creating moredarkness. In this example of an embedded optical product 10′, elementsE₁, E₂, . . . E_(n) with steep enough slopes can cause light to betotally internally reflected within the substrate (which has a higherindex than the surrounding medium), and creating even more darkness.

FIG. 1E is another example optical product 10′ in accordance withcertain embodiments described herein. As shown in FIG. 1E, the opticalproduct 10′ can include a plurality of portions P′₁, P′₂, . . . P′_(n).Each portion P′₁ can include elements E₁, E₂, . . . E_(n), e.g.,non-holographic elements, on the optical product 10′. As describedherein, utilizing embodiments of the optical product 10′ having elementsE₁, E₂, . . . E_(n) (or masters having features F₁, F₂, . . . F_(n))with smaller height can be advantageous to reduce the amount of materialused. However in cases where height is less important, certainembodiments can utilize elements E₁, E₂, . . . E_(n) with slowly varyingsurfaces (e.g., slopes) creating a substantially contiguous surface fromone portion P′_(n) to another. In various embodiments, the number ofsubstantially contiguous portions can include at least two, three, four,five, eight, ten, fifteen, twenty, or more, or be in any range inbetween these values.

Various methods can be used to manufacture the master 10 for fabricatingan optical product 10′. An example method 100 is shown in FIG. 2. Asshown in operational block 110, the method 100 can include providing adata file, e.g., a 2D data file, configured to describe, characterize,and/or record features the 3D object and/or 3D image 50′. The data filecan provide the pattern of the features F₁, F₂, . . . F_(n) on thesurface 12 of the master 10.

For example, the data file can comprise a plurality of portions (as willbe described further herein). Each portion can correspond to one or morepoints on a surface S of the 3D object 50. Each portion can comprisefeatures of intensity corresponding to non-holographic elements on theoptical product 10′. A gradient in intensity can correlate to aninclination of the surface S of the 3D object 50 at the one or morecorresponding points. In addition, an orientation of the features cancorrelate to an orientation of the surface S of the 3D object 50 at theone or more corresponding points. As shown in operational block 120, themethod 100 can further include manufacturing the master 10 based atleast in part on the 2D data file.

As described herein, certain embodiments of the optical product 10′ canproduce a bright, mirror-like image. In some implementations, a mattefinish may be desired. FIG. 2A illustrates an example method that can beused to manufacture a surface relief diffuser and also to determine aheight displacement file used to manufacture the diffuser. In the method200 shown in FIG. 2A, an input image 210 of the 3D object 50 (e.g., a 2Dphotograph of the 3D object) is entered into the recording loop 220 ofthe main program 225 of the processor 230. Other information, such asuser parameters 211 (e.g., angle, scale, zoom, etc.), exposurecompensation curve 212, intensity compensation mask 213, and apodizingmask 214 can also be entered into the recording loop 220. The processor230 can produce a height displacement file 240 that is configured todescribe the intensities of the 3D object 50. This height displacementfile 240 can be used as a map to generate the pattern of the diffuser.In some examples of the height displacement file 240, the intensities ofthe 3D object can be correlated to a depth for the diffuser. Forexample, the black sections of the 3D object 50 can correlate to thesurface of the diffuser, white sections of the 3D object 50 cancorrelate to a lower depth (e.g., down 10 μm), and grey sections of the3D object 50 can correlate to some depth in between. Other variationsare possible.

In the example method 200 shown in FIG. 2A, a digital micromirror device(DMD) video projector 250 can be used along with the photoresistrecording plate 260, each receiving the inputted information from therecording loop 220. The DMD video projector 250 includes a DMD chip thatincludes a plurality of micromirrors that in certain embodiments cancorrespond to the pixels of the height displacement file 240. The pixelsof the height displacement file 240 can also correspond to the regionson the X-Y stage of the photoresist recording plate 260 in someembodiments. Each micromirror of the DMD chip can be used as a spatiallight modulator that, for example, reflects light from a light source inthe video projector 250 in the on-state, and that does not reflect lightin the off-state. Varying the amount of light intensity can be producedby varying the time the micromirror is in the on- and off-states (e.g.,pulse width modulation, etc.). As shown in FIG. 2A, demagnificationoptics 255 can be used to produce the pattern of the diffuser in a lightsensitive material, e.g., a photoresist, on the resist recording plate260. In some embodiments, the resist can be used as the diffuser. Asdisclosed herein, other techniques, such as electron beam lithography onelectron sensitive material and ion beam lithography on ion sensitivematerial can also be used. Certain embodiments of the diffuser can beused with certain embodiments of the optical product 10′ to produce adiffuse or hazy layer over the reflected image 50′ to produce an imagewith a matte finish.

FIG. 2B illustrates an example method that can be used to manufacturethe master 10 and also to determine the data file to be used tomanufacture the master 10, e.g., to determine the pattern of thefeatures F₁, F₂, . . . F_(n) on the surface 12 of the master 10. Certainsuch embodiments can be advantageous as a 3D physical object and/or a 3Dmodel utilizing physical dimensions of the 3D object (e.g.,topographical calculations) are not required. For example, in the method300 shown in FIG. 2B, the input image 305 can be a 2D input image (e.g.,a 2D photograph of the 3D object) or 2D image converted from a 3D image.In some embodiments, the input image 305 can be converted into a 2Dinterpolated image 308 and produced as a 2D converted image 310. The 2Dimage of the 3D object can be translated into a gray scale image (e.g.,a normal map 315 wherein black, white, and gray regions correlate todifferent heights of the 3D object). In the method 300 shown in FIG. 2B,the converted image 310 (or a normal map 315) is entered into therecording loop 320 of the main program 325 of the processor 330 inaccordance with certain embodiments described herein. Similar to themethod 200 in FIG. 2A, other information, such as user parameters 311(e.g., angle, scale, zoom, etc.), exposure compensation curve 312,intensity compensation mask 313, and apodizing mask 314 can also beentered into the recording loop 320. The processor 330 can produce adata file 340, e.g., a 2D data file, that is configured to describe the3D image 50′ of at least a part of the 3D object 50. In someembodiments, the intensities in the data file 340 can be assigned basedon gray scale. For example, the data file 340 can comprise a pluralityof portions. Each portion can correspond to one or more points on asurface S of the 3D object 50. Each portion can comprise features ofintensity corresponding to non-holographic elements on the opticalproduct 10′. A gradient in intensity can correlate to a gradient or aninclination of the surface S of the 3D object 50 at the one or morecorresponding points. In addition, an orientation of the features cancorrelate to an orientation of the surface S of the 3D object 50 at theone or more corresponding points. This data file 340 can be used as amap to generate the pattern of features F₁, F₂, . . . F_(n) on thesurface 12 of the master 10. An example data file is discussed withrespect to FIG. 3A.

Similar to method 200 in FIG. 2A, a digital micromirror device (DMD)video projector 350 can be used along with the photoresist recordingplate 360, each receiving the inputted information from the recordingloop 320. The plurality of micromirrors in the DMD video projector 350in certain embodiments can correspond to the pixels of the data file240. The pixels of the data file 340 can also correspond to one or moreportions P₁, P₂, . . . P_(n) of the surface 12 of the master 10 in someembodiments. As shown in FIG. 2B, the demagnification optics 355 can beused to produce the pattern of features F₁, F₂, . . . F_(n) in a lightsensitive material, e.g., a photoresist, on the resist recording plate360. In some embodiments, the resist can be used as the surface 12 ofthe master 10. As disclosed herein, other techniques, such as electronbeam lithography on electron sensitive material and ion beam lithographyon ion sensitive material can also be used.

In some embodiments, the method 300 can further include adding on themaster 10 features corresponding to holographic elements on the opticalproduct 10′. For example, an optical recording (e.g., a planar opticalrecording) for the holographic elements can be superimposed onto themaster 10 to add the holographic elements on the master 10. As anotherexample, in some embodiments, the data file 340 can include featurescorresponding to holographic elements on the optical product 10′. Inother embodiments, a separate data file comprising the features ofintensity corresponding to holographic elements on the optical product10′ can be provided. Manufacturing the master 10 can be based at leastin part on the data file 340 including features corresponding tonon-holographic elements and on the data file including featurescorresponding to holographic elements on. In some such embodiments, thedata file 340 including the features corresponding to non-holographicelements and the data file including the features corresponding toholographic elements can be used sequentially or simultaneously tomanufacture the master 10. In some other embodiments, a needle, such asfrom an atomic force microscope, can be used to produce the featurescorresponding to the holographic elements on the optical product 10′.Other methods can be employed to add holographic features or elements.

FIG. 2C illustrates yet another example method that can be used todetermine the pattern of the features F₁, F₂, . . . F_(n) on the surface12 of the master 10. The method 400 shown in FIG. 2C is similar to themethod 300 shown in FIG. 2B except that a normal map 415 can be providedinstead of the input image 310. The normal map 415 can be inputted intothe main program 425 of the processor 430 to produce the data file 440.

FIG. 3A illustrates an example 2D data file 540 in accordance withcertain embodiments disclosed herein. The data file 540 can include aplurality of portions p₁, p₂, . . . p_(n). In some embodiments, theplurality of portions p₁, p₂, . . . p_(n) can form a single cell (e.g.,a mono-cell). In other embodiments, as shown in FIG. 3A, the pluralityof portions p₁, p₂, . . . p_(n) can form a plurality of cells. Invarious embodiments, the portions p₁, p₂, . . . p_(n) can form apixelated surface corresponding to the portions P₁, P₂, . . . P_(n) ofthe surface 12 of the master 10. For example, as shown in FIG. 3A, theportions p₁, p₂, . . . p_(n) can include a plurality of rows andcolumns.

As also shown in FIG. 3A, in some embodiments, borders 13′ can surroundat least part of the portions p₁, p₂, . . . p_(n). The borders 13′ cansubstantially surround a portion p_(n) or can surround just part of aportion p_(n). As with the master 10, the size and shape of the portionsp₁, p₂, . . . p_(n) on the data file 540 are not particularly limited.Some of the portions p₁, p₂, . . . p_(n) can comprise a symmetricalshape. For example, the symmetrical shape can include a rectangle, asquare, a rhombus, an equilateral triangle, an isosceles triangle, aregular polygon (e.g., a regular pentagon, a regular hexagon, a regularoctagon), etc. The shape can also include curvature, e.g., a circle, anellipse, etc. In other embodiments, some of the portions p₁, p₂, . . .p_(n) can comprise a non-symmetrical shape, e.g., a non-rotationallysymmetrical shape, and/or an irregular shape. For example, FIG. 3Billustrates an example embodiment of a data file 545 with irregularlyshaped portions p₁, p₂, . . . p_(n). In some embodiments, some of theportions p₁, p₂, . . . p_(n) can have a shape that is substantially thesame as other portions p₁, p₂, . . . p_(n). In other embodiments, e.g.,as shown in FIG. 3B, some of the portions p₁, p₂, pu can have a shapethat is different from other portions p₁, p₂, . . . p_(n).

As with the master 10, the arrangement of the portions p₁, p₂, . . .p_(n) in the data file 540 is not particularly limited. For example,whether with or without borders, whether symmetrically shaped ornon-symmetrically shaped, or whether regularly or irregularly shaped,the portions p₁, p₂, . . . p_(n) can form a periodic array. For example,in FIG. 3A, the portions p₁, p₂, . . . p_(n) form a periodic array. Inother embodiments, whether with or without borders, whethersymmetrically shaped or non-symmetrically shaped, or whether regularlyor irregularly shaped, the portions p₁, p₂, . . . pu can form anaperiodic array. For example, in FIG. 3B, the portions p₁, p₂, . . .p_(n) form an aperiodic array. In yet other embodiments, the portionsp₁, p₂, . . . p_(n) can form a combination of periodic and aperiodicarrays.

With continued reference to FIG. 3A, each portion p_(n) can includefeatures f₁, f₂, . . . f_(n) that correspond to features F₁, F₂, . . .F_(n) on the surface 12 of the master 10. Portion p_(a) has a singlefeature f₁, while portion p_(b) has multiple features f_(n). Thefeatures f₁, f₂, . . . f_(n) of the data file 540 can include featuresof intensity (varying dark and light lines). In some embodiments, theintensity can correlate to the height of a feature on the surface S ofthe 3D object 50.

In various embodiments, a lateral distance between two features can bedefined in some embodiments as a pitch. In some embodiments, the pitchbetween features within a portion p_(n) can be substantially the samewithin the portion p_(n). For example, in various embodiments, inportion p₁ of the portions p₁, p₂, . . . p_(n), the feature f₁ cancomprise a plurality of features that form a periodic array such thatthe pitch is substantially the same within portion p₁. In addition, insome embodiments, the features f₁, f₂, . . . f_(n) among multipleportions p₁, p₂, . . . p_(n), can form a periodic array such that thepitch is substantially the same among multiple portions p₁, p₂, . . .p_(n).

In other embodiments, the features can form an aperiodic array such thatthe pitch may be different among multiple portions p₁, p₂, . . . p_(n).However, although the pitch may be different for different portions p₁,p₂, . . . p_(n), in some embodiments, the pitch can be slowly varying(e.g., less than 15% change per lateral distance, less than 12% changeper lateral distance, less than 10% change per lateral distance, lessthan 8% change per lateral distance, less than 5% change per lateraldistance, less than 3% change per lateral distance, or less than 1%change per lateral distance) among the portions p₁, p₂, . . . p_(n). Insome embodiments, the pitch may uniformly change across multipleportions p₁, p₂, . . . p_(n).

In other embodiments, the features could be chirped within a portion pusuch that the pitch may be different within the portion p_(n). In somesuch embodiments, the pitch within the portion p_(n) may slowly vary(e.g., less than 15% change per lateral distance, less than 12% changeper lateral distance, less than 10% change per lateral distance, lessthan 8% change per lateral distance, less than 5% change per lateraldistance, less than 3% change per lateral distance, or less than 1%change per lateral distance).

FIG. 3A shows an example data file 540 with linear features where thepitch is substantially uniform within a portion pu, and FIG. 3B shows anexample data file 545 with curved features where the pitch issubstantially uniform within a portion p_(n). FIG. 3A is also an exampleof features having a pitch that slowly changes (e.g., less than 10%change per lateral distance) across multiple portions p₁, p₂, . . .p_(n).

In various embodiments, each feature of intensity can include a slope.Various embodiments can advantageously have a uniform gradient (e.g.,uniform slope) within each portion p_(n) such that the gradient is asingle value (e.g., a single polar angle θ_(n)) at the correspondingpoint S_(n) on the surface S of the 3D object 50. The gradient in thefeatures f₁, f₂, . . . f_(n) can correlate to an inclination of thesurface S of the 3D object 50 at the corresponding point S₁, S₂, . . .S_(n). In other embodiments, the feature f_(n) within a portion p_(n)includes a plurality of features, and the features within the portionp_(n) may have more than one gradient (e.g., different slopes). In suchembodiments, the average gradient (e.g., average slope) of the featureswithin the portion p_(n) can correlate to the inclination of the surfaceS of the 3D object 50 at the corresponding point S_(n).

Various embodiments can also advantageously have a uniform orientationwithin each portion pu, such that the orientation is a single value(e.g., a single azimuth angle φ_(n)) at the corresponding point S_(n) onthe surface S of the 3D object 50. In various embodiments, theorientation of features f₁, f₂, . . . f_(n) can correlate to anorientation of the surface S of the 3D object 50 at the correspondingpoint S₁, S₂, . . . S_(n). In other embodiments, the feature f_(n)within a portion p_(n) includes a plurality of features, and thefeatures within the portion p_(n) may have more than one orientation(e.g., different orientations). In such embodiments, the averageorientation of the features within the portion p_(n) can correlate tothe orientation of the surface S of the 3D object 50 at thecorresponding point S_(n). Furthermore, the orientation of the featureswithin and among the portions p₁, p₂, . . . p_(n), can slowly vary(e.g., less than 15% change per lateral distance, less than 12% changeper lateral distance, less than 10% change per lateral distance, lessthan 8% change per lateral distance, less than 5% change per lateraldistance, less than 3% change per lateral distance, or less than 1%change per lateral distance) within and among the portions p₁, p₂, . . .p_(n).

In some embodiments, where a feature f₁ includes multiple featureswithin a portion, the features can appear discontinuous with otherfeatures within the portion. In some embodiments where the surface 12 ofthe master 10 is pixelated (e.g., having a plurality of cells), thefeatures f₁, f₂, . . . f_(n) can appear discontinuous with features insurrounding adjacent portions. Based on pixel or cell size and/ortolerances in creating the data file 540, some embodiments may includerandom discontinuities with substantially no (relatively little if any)negative impact in image reproduction. Such discontinuity can reduceiridescence. In other embodiments, the portions p₁, p₂, . . . p_(n) canform a single cell or a mono-cell. In some such embodiments, thefeatures f₁, f₂, . . . f_(n) can appear continuous and smoothly varyingdepending on the shape. In other such embodiments, the features f₁, f₂,. . . f_(n) can appear discontinuous due to discontinuities in the 3Dobject 50.

In some embodiments, as shown in FIG. 3C, the features f₁, f₂, . . .f_(n) can comprise linear features corresponding to a substantiallysmooth region of the surface S of the 3D object 50. The features f₁, f₂,. . . f_(n) can be used to produce linear features F₁, F₂, . . . F_(n)on the surface 12 of the master 10. The features f₁, f₂, . . . f_(n) canalso be used to produce non-linear features F₁, F₂, . . . F_(n) on thesurface 12 of the master 10. In some embodiments, features f₁, f₂, . . .f_(n) that are linear can be used to correspond to a curved region ofthe surface S of the 3D object 50. In some such embodiments, linearfeatures f₁, f₂, . . . f_(n) in the data file can be used to represent acurved region by using a piecewise approximation function.

As shown in FIG. 3D, in some embodiments, although linear features f₁,f₂, . . . f_(n) in the data file can correspond to a substantiallysmooth region of the surface S of the 3D object 50, non-linear featureson the master 10 (e.g., curved facets shown in left profile) can beused. As described herein, in some such embodiments, non-linear featureson the master 10 can be used to produce elements E₁, E₂, . . . E_(n) onan optical product 10′ that can appear smooth because the correspondingfeatures on the optical product 10′ can be relatively small (e.g.,between 1 μm and 100 μm, between 1 μm and 75 μm, between 1 μm and 50 μm,or between 1 μm and 25 μm).

As the features f₁, f₂, . . . f_(n) of the data file 540 correspond toaspects of the surface S of the 3D object 50, the features f₁, f₂, . . .f_(n) of the data file 540 can be used to produce the features F₁, F₂, .. . F_(n) on the surface 12 of the master 10. As described herein, thefeatures F₁, F₂, . . . F_(n) on the surface 12 of the master 10 can beused to fabricate the elements E₁, E₂, . . . E_(n) on the surface 12′ ofthe optical product 10′. As described herein, in various embodiments,the elements E₁, E₂, . . . E_(n) on the optical product 10′ can benon-holographic. For example, the elements E₁, E₂, . . . E_(n) do notneed to rely on holography to render a 3D image 50′ of the 3D object 50.

FIG. 4A is another example 2D data file 640 prepared in accordance withcertain embodiments described herein. The data file 640 was generated bythe normal map 650 shown in FIG. 4B. As an example, the lower leftportion 645 of the data file 640 represents the center of thehemispherical object 655 in the lower left portion of the normal map650. The data file 640 was used to generate the features F₁, F₂, . . .F_(n) on the surface 12 of a master 10, which was used to fabricate theelements E₁, E₂, . . . E_(n) on the surface 12′ of an optical product10′. The optical product 10′ was configured, when illuminated, toreproduce by reflected light, the 3D image 650′ shown in FIG. 4C.

In certain embodiments, an optical product 10′ is also disclosed herein.As described herein, the optical product 10′ can be configured, whenilluminated, to reproduce by reflected light, a 3D image 50′ of at leasta part of a 3D object 50. As shown in FIG. 1A, similar to the master 10,the optical product 10′ can include a surface 12′ comprising a pluralityof portions P′₁, P′₂, . . . P′_(n). Each portion P′_(n) can correspondto a point S_(n) on a surface S of the 3D object 50. Each portion P′_(n)can comprise features, e.g., non-holographic elements E₁, E₂, . . .E_(n). In certain embodiments, the non-holographic elements E₁, E₂, . .. E_(n) can be configured to produce at least part of the 3D image 50′without relying on diffraction. In various embodiments, the portionsP′₁, P′₂, . . . P′_(n) can form a single cell (e.g., a mono-cell). Inother embodiments, the portions P′₁, P′₂, . . . P′_(n) can form aplurality of cells. Each portion P′_(n) can form a cell of the pluralityof cells. The optical product 10′ can include borders surrounding atleast part of the portions P′₁, P′₂, . . . P′_(n).

A gradient (e.g., uniform slope or average slope) in the non-holographicfeatures E₁, E₂, . . . E_(n) can correlate to an inclination of thesurface S of the 3D object 50 at the corresponding point S₁, S₂, . . .S_(n). In addition, the orientation (e.g., uniform orientation oraverage orientation) of the non-holographic features E₁, E₂, . . . E_(n)can correlate to an orientation of the surface S of the 3D object 50 atthe corresponding point S₁, S₂, . . . S_(n).

Furthermore, since the master 10 can be used to fabricate an opticalproduct 10′, aspects disclosed herein with reference to the master 10can apply to certain embodiments of the optical product 10′. Forexample, disclosure with respect to the shapes (e.g., symmetrical,non-symmetrical, irregular, curved, etc.) and arrangements (e.g.,periodic, aperiodic, etc.) of the portions P₁, P₂, . . . P_(n) for themaster 10 can apply to the shapes and arrangements of the portions P′₁,P′₂, . . . P′_(n) of the optical product 10′. As another example,disclosure with respect to the features F₁, F₂, . . . F_(n) (e.g.,linear, curved, periodic, aperiodic, slowly varying, continuous,discontinuous, non-sinusoidal, etc.) for the master 10 can apply to thefeatures E₁, E₂, . . . E_(n) of the optical product 10′. Furthermore, asdescribed herein with respect to the master and the method ofmanufacturing the master, the optical product 10′ of certain embodimentscan further comprise features corresponding to holographic features.

In addition, small features can be imbedded in the optical product 10′that do not contribute to the formation of the image. Such imbeddedfeatures can be used in authenticity and security applications.Furthermore, as described herein, certain embodiments can incorporateintentional variations within one or more portions P′₁, P′₂, . . .P′_(n) of the optical product 10′ for security applications. OpticalProducts Comprising Non-Holographic Features and Interference OpticalStructures

Although some implementations described herein include optical productsconfigured, when illuminated, to reproduce by reflected or transmittedlight, a 3D image, various implementations can reproduce a 3D image inboth reflection and transmission. In particular, some implementationscan reproduce the 3D image in a first color in transmission mode and asecond color in reflection mode. The second color can be different fromthe first color. In addition, although some implementations describedherein include optical products configured to reduce and/or eliminatecolor change with angle of tilt (e.g., reducing and/or eliminatingiridescence by using non-holographic features), in some instances, itmay be desired to provide a color change with viewing angle.Accordingly, various implementations can comprise an interferenceoptical structure disposed on one or more non-holographic featuresdescribed herein. Various implementations can have color shiftingproperties. The optical product can be configured to provideauthenticity verification on an item for anti-counterfeiting orsecurity. The item can be a banknote, a credit card, a debit card, astock certificate, a passport, a driver's license, an identificationcard, a document, a tamper evident container or packaging, consumerpackaging, a bottle of pharmaceuticals, etc. The item can beelectronics, apparel, jewelry, cosmetics, a handbag, etc.

To curtail counterfeiting, currency, documents (e.g., banknotes) as wellas other items such as products and packaging can be provided withsecurity features that can be inspected by the general public to verifyauthenticity. In many cases, it can be advantageous if the securityfeatures can be easily seen under a variety of light conditions andwithout the need for special lighting conditions. It can also bedesirable that the security features have distinct characteristics thatcan be easily identified by the public within a 1-10 second time frame.In addition, it is advantageous in general, if the security feature isnot susceptible to copying by electronic or photographic equipment, suchas, for example, printers, copiers, cameras, etc.

One example of a security feature employed in banknotes is thewatermark, which has a fairly high degree of awareness among the generalpublic. An example of a watermark can be an image comprising light anddark regions that can be easily seen by holding up the banknote to seethe watermark in light transmission. However, watermarks may besusceptible to be copied and thus are not very secure. Other examples ofsecurity features may use inks and motion type features that are notreadily seen under low light conditions (e.g., at low lit bars,restaurants, etc.), have poor image resolution, and/or have slow opticalmovement relative to the movement of the banknote. Accordingly, someexisting security features tend to be more complicated structures havingmore complex color changing effects. This approach, however, can bedisadvantageous when the complicated security devices are applied tobanknotes or currency, as these complicated security devices may confusean average person who is looking for a distinctive security feature.

Having a security feature (e.g., an anti-counterfeit feature) that hashigh contrast with respect to the background that can be easilyidentified by the general public under a variety of light conditions,including low light, can be advantageous. Accordingly, various opticalproducts disclosed can reproduce a 3D image in color in reflectionand/or transmission. In various instances, the image can appear to haveone color in reflection and another different color in transmission.These security features can be incorporated in a consumer product,packaging, or a document (e.g., banknote). A consumer, merchant, or abank teller can holdup such a banknote to light to readily verify theauthenticity of the banknote. Additionally or alternatively, in someimplementations, the security feature can be configured to exhibit colorshift and/or movement of identifiable features when the viewing angle isvaried to enhance security. These and other features are described infurther detail herein.

Accordingly, various security features contemplated herein can compriseoptical stacks and/or structures that are at least partially reflectiveand at least partially transmissive. The security features contemplatedherein can be configured as coatings, threads, laminates, foils, films,hot stamps, windows, patches, labels, pigments and/or inks disposed onone or more non-holographic features and incorporated with documents(e.g., banknotes), packaging, or other items. The innovative aspectsdescribed in this application also include systems and methods offabricating optical products comprising one or more non-holographicfeatures with optical structures and/or stacks that are at leastpartially reflective and at least partially transmissive. In someembodiments, such optical structures may be fabricated on support orbase layers or sheets such as webs (e.g., roll coated webs). Processesdescribed herein may also include removing the fabricated opticalstructures and/or stacks from a support or base layer (e.g., roll orsheet). The innovative aspects described in this application furtherinclude methods and systems for including the optical structures and/orstacks that are at least partially reflective and at least partiallytransmissive in pigment and inks having a desired amount of durabilityand mechanical strength to be disposed on one or more non-holographicfeatures and to be further used in or on or incorporated into banknotesand other security devices/documents. The innovative aspects describedin this application further include methods and systems for includingthe optical structures and/or stacks (e.g., in the form of a hot stampcoating, a foil coating, or an ink coating) to be disposed on one ormore non-holographic features and to be further used in or on orincorporated into documents or packaging. In some implementations, adocument or packaging can include a main body and the optical structurecan be disposed on the main body. The main body can comprise cloth,paper, plastic, cardboard, etc.

FIG. 5 schematically illustrates a cross-sectional view of an exampleoptical product 1100 with an interference optical structure 1130 (e.g.,a coating, film, pigment, etc.) disposed on non-holographic features1120. The optical product 1100 can be configured, when illuminated, toreproduce an image that appears 3D of at least a part of a 3D object(e.g., a regularly or irregularly shaped object). The optical product1100 can include a surface 1111 (e.g., a surface of a substrate 1110described herein) comprising a plurality of portions, each portioncorresponding to a point on a surface of the 3D object (e.g., asdescribed with respect to FIGS. 1A-4C). The optical product 1100 canalso include one or more non-holographic features 1120 (e.g., linearand/or curved facets with various angles, orientations, and heights)disposed within each portion configured to produce at least a part ofthe image without relying on diffraction (e.g., as described withrespect to FIGS. 1A-4C). An interference optical structure 1130 (e.g., acoating, film, pigment, etc.) can be disposed on one or morenon-holographic features 1120. In various implementations, theinterference optical structure 1130 can be disposed with respect to oneor more non-holographic features 1120 such that the optical product1100, when illuminated, reproduces color in transmission mode T and/orreflection mode R. As an example, the interference optical structure1130 can be disposed with respect to one or more non-holographicfeatures 1120 such that the optical product 1100, when illuminated,reproduces the image in a first color in transmission mode T and asecond color in reflection mode R. The second color in reflection mode Rcan be different from the first color in transmission mode T. In someinstances, the first and second colors can be complementary colors. Insome instances, the first and second colors are not complementarycolors.

In some instances, the optical product 1100 can include a transparent oroptically transmissive window 1145 in an item such as a document. Thewindow 1145 can be adhered to the non-holographic features 1120 andinterference optical structure 1130 with an adhesive 1140 in variousimplementations.

FIG. 6 schematically illustrates the non-holographic features 1120 andinterference optical structure 1130 of the example optical product 1100producing colored depth perception in the reproduced image of theobject. As described herein, the non-holographic features 1120 caninclude discontinuities (e.g., discontinuous with other features). Insome instances, the discontinuous features can correspond to acontinuous region of the object. As described herein, thenon-holographic features 1120 with less steep slopes can be configuredto reflect light toward an observer's eye, and the non-holographicfeatures 1120 with steeper slopes are configured to reflect light awayfrom the observer's eye. In section 1121, the non-holographic features1120 include multi-angled facets with different slopes, orientations,and heights. For individual ones of the portions in section 1121, agradient in the non-holographic features 1120 can correlate to a surfacenormal of the surface of the 3D object at the corresponding point. Forindividual ones of the portions in section 1121, an orientation of thenon-holographic features 1120 can correlate to an orientation of thesurface of the 3D object at the corresponding point. Accordingly, thenon-holographic features 1120 can produce the appearance of the 3D imageand the interference optical structure 1130 can provide color in theimage. In section 1122, the non-holographic features 1120 have the same(e.g., substantially the same) slopes which may produce no image and theinterference optical structure 1130 can provide the same (e.g.,substantially the same) color to the observer. In section 1122, no imagein the same (e.g., substantially the same) color can also be producedwith the interference optical structure 1130 disposed on a flat area(e.g., no facets).

Various implementations can create various optical effects utilizing acombination of non-holographic features 1120 with interference opticalstructures 1130 along with other features described herein (and/or otherfeatures known in the art or yet to be developed). For example, someimplementations can also utilize reflective structures and/ordemetallized structures.

FIG. 7A shows an example planar view 1150A of a reproduced object 1151Aand background 1152A. The image that appears three dimensional can beformed by the non-holographic features 1120 described herein. Asdescribed herein, the non-holographic features 1120 can be coated with areflective material. In this example, the non-holographic features 1120and surrounding areas were coated with aluminum. The non-holographicfeatures 1120 can be de-metallized (e.g., leaving the surrounding areasmetallized) and coated with an interference optical structure 1130. Inthis example, the non-holographic features 1120 were de-metallized andcoated with an interference optical structure 1130. In FIG. 7A, theimage of the object 1151A (e.g., a mustang in this example) is producedin color with an aluminum background. In some instances, theinterference optical structure 1130 can be partially transmissive andpartially reflective such that the object 1151A appears one color intransmission and another color in reflection. For example, when viewingthe optical product from the other side, the object 1151A may beproduced in a different color. In some implementations, the background1152A, e.g., instead of the object 1151A, can also be produced with aninterference optical structure 1130. In some implementations, thebackground 1152A, e.g., in addition to the object 1151A, can also beproduced with an interference optical structure 1130 (e.g., anotherinterference optical structure).

FIG. 7B shows another example planar view 1150B of a reproduced object1151B and background 1152B. In this example, the color in the image ofthe object 1151B (e.g., a mustang in this example) is produced by analuminum coating and the background 1152B is produced with aninterference optical structure 1130 deposited onto flat ornon-holographic features 1120 with the same (e.g., substantially thesame) slopes, orientations, and heights. In FIG. 7B, the background1152B is produced in color. In some instances, the interference opticalstructure 1130 can be partially transmissive and partially reflectivesuch that the background 1152B appears one color in transmission andanother color in reflection. For example, when viewing the opticalproduct from the other side, the background 1152B may be produced in adifferent color.

FIG. 8 shows another example planar view 1150C of a reproduced object1151C and background 1152C. The color in the image of the object 1151C(e.g., mustang in this example) is produced by an interference opticalstructure 1130 (e.g., similar to FIG. 7A) and the background 1152C isproduced with an aluminum coating deposited onto flat or non-holographicfeatures 1120 with the same (e.g., substantially the same) slopes,orientations, and heights. In addition, portions of the background 1152Ccan include de-metallized regions 1153C. In this example, portions ofthe aluminum was de-metallized to produce alphanumeric characters. Thede-metallized regions 1153C can also be formed into other objects(regular or irregularly shaped objects), patterns, or images, etc.

FIG. 9 shows another example planar view 1150D of a reproduced object1151D and background 1152D. In this example, the colors in the image ofthe object 1151D and the background 1152D are produced by one or moreinterference optical structures (e.g., one or more interference opticalstructures). As described herein, various interference opticalstructures 1130 can operate in reflection and/or transmission modes. Insome implementations, the optical structure 1130 can produce color inreflection and/or transmission. In some instances, the optical structure1130 can produce a first color in transmission mode and a second colorin reflection mode. In the example shown in FIG. 9, the color of theimage of the object 1151D (e.g., a “10” in this example) is produced byan interference optical structure 1130 in reflection mode, and the colorof the background 1152D is produced by the interference opticalstructure 1130 in transmission mode. In this example, at a certainviewing angle, the color in reflection is different from the color intransmission. In some instances, the interference optical structure 1130can be partially transmissive and partially reflective such that theobject 1151D and the background 1152D appear one color in transmissionand another color in reflection. For example, when viewing the opticalproduct from the other side, the object 1151D and the background 1152Dmay be produced in different colors.

In some instances, the optical structure 1130 can have color shiftingproperties. For example, the color in transmission and/or reflection canchange with a change in viewing angle. With respect to FIG. 9, at adifferent viewing angle, the optical structure can produce anotherdifferent color in transmission mode and another different color inreflection mode. In some instances, the optical structure 1130 can havenon-color shifting properties. For example, the color in transmissionand/or reflection might not change with a change in viewing angle.

FIG. 10 shows another example view 1150E of a reproduced object andbackground. This example illustrates the optical effect of a coloroutline or halo 1155 that appear to be on the surface of the object,which provides another difficulty of being counterfeited. Such effectcan be produced by an interference optical structure 1130 disposed onnon-holographic features 1120.

Some implementations can utilize reflective structures, demetallizedstructures, and/or interference optical structures in combination. Forexample, the non-holographic features and the surrounding areas can becoated with a reflective material (e.g., metallized). Some portions ofthe non-holographic features and/or surrounding areas can bede-metallized. Portions metallized and de-metallized can then be coatedwith an interference optical structure.

Various interference optical structures will now be described.

The interference structures described herein may comprise structuresthat produce optical interference. Such structures may include aplurality of reflective surfaces from which light reflects. Light fromone such reflective surface may, for example interfere with light fromanother such reflective surface and produce optical interference.

In certain implementations, the optical structure 1130 can comprise aFabry-Perot or an etalon structure. The etalon structure may comprisefor example two (e.g., first and second) reflective surfaces separatedby a distance. Light incident on the etalon may reflect off the tworeflective surfaces. The distance between the first and secondreflective surfaces may introduce phase shift between the lightreflected from the first reflected surface and light reflected from thesecond reflective surfaces. This phase shift may produce opticalinterference. Accordingly, light reflected from the etalon may haveproperties associated with interference. For example, the lightreflected may have a particular wavelength spectrum and may for examplebe a particular color. In some implementations, the etalon may exhibitcolor shifting, the color of reflected light changing color with theangle of the incident light and/or the angle of viewing the etalon.Etalons may also produce interference in transmission as well. Likewisethe light transmitted through the etalon may have properties associatedwith interference such as a characteristic wavelength or spectralcharacter (e.g., a particular spectral band or color), change in colorwith angle of incidence of light and/or angle of viewing, etc. In someimplementations the etalon comprises a plurality of layer stacked on topof each other the for the first and second reflective surfaces spacedapart by a distance (e.g., the thickness of one of the layers).

Light reflected from more than two reflective surfaces can alsointerfere with each other to produce an optical interference effect.Accordingly, in various implementations, the optical structure maycomprise a plurality of layers such as two or more. Without subscribingto any particular scientific theory, in some cases the plurality oflayers may provide a plurality of reflective surfaces, for example, atthe interface between the layer. Similarly, in various implementations,the optical structure 1130 can comprise an interference optical stack.In some implementations, the optical stack may include pairs of high (H)and low (L) index layers comprising materials having higher and lowerreflective index, respectively. In various implementations the differentlayer have thickness to provide interference and the desiredinterference effect.

In various implementations, for example, the optical structure 1130 cancomprise a A/D/M multilayer thin film optical stack, where A is anabsorber layer, D is a transparent dielectric layer, and M is a metallayer, for example, that is opaque. In some instances, the absorberlayer can have a ratio of the real part (n) of the refractive index tothe imaginary part (k) of the refractive index near unity. In someimplementations, the optical structure can comprise a A/D/M/D/Amultilayer thin film optical stack. As another example, the opticalstructure can comprise a A/D/M/M*/M/D/A multilayer thin film opticalstack, where M* is a magnetic layer. Some such structures can includethose described in U.S. Pat. Nos. 4,705,300 and 6,838,166, each of whichis incorporated herein by reference in its entirety.

The optical structure 1130 can also comprise, for example, a M/D/M orD/M/D/M/D multilayer thin film optical stack, where D is a transparentor optically transmissive dielectric layer and M is a metal layer. Insome implementations, the metal layer can have a ratio of the real part(n) of the refractive index to the imaginary part (k) of the refractiveindex greater than or equal to 0.01 and less than or equal to 0.5, 0.4,or 0.2.

In various implementations, the optical structure 1130 can comprise aD/M/D or M/D/M/D/M multilayer thin film optical stack, where D is atransparent or optically transmissive dielectric layer and M is a metallayer. In some instances, the metal layer can have a ratio of the realpart (n) of the refractive index to the imaginary part (k) of therefractive index greater than or equal to 0.01 and less than or equal to0.5, 0.4, or 0.2. In some instances, individual ones of the metal layerscan have a thickness of about 20 nm, 30 nm, 40 nm, 50 nm, 60 nm, 70 nm,80 nm, 90 nm, 100 nm, or any ranges formed by such values, e.g., fromabout 20 nm to about 100 nm.

The metal layers can, for example, be any of those described herein,e.g., one or more of the metal layer can comprise aluminum, silver,gold, silver alloy, or gold alloy. The dielectric layers can, forexample, be any of those described herein, e.g., one or more of thedielectric layers can comprise magnesium fluoride, silicon dioxide, zincoxide, zinc sulfide, zirconium dioxide, titanium dioxide, tantalumpentoxide, ceric oxide, yttrium oxide, indium oxide, tin oxide, indiumtin oxide, aluminum oxide, tungsten trioxide, or combinations thereof.In some instances, one or more of the dielectric layers can comprise anorganic layer.

In various implementations, the optical structure 1130 can comprise aH/L/H/L/H multilayer thin film optical stack, where H and L are layerswith a refractive index and the H layers have a higher refractive indexthan the L layers. In some designs, the L layers have a refractive indexless than 1.65 and the H layers have a refractive index greater than orequal to 1.65. Some such structures can, for example, include thosedescribed in U.S. Pat. No. 6,838,166, which is incorporated herein byreference in its entirety.

Some such optical structures 1130 will be described further herein.

Optical Structures Comprising Metal Layers Surrounded by DielectricLayers (e.g., D/M/D/M/D Optical Stack)

FIG. 11 schematically illustrates an optical structure 10 comprising astack of layers that can be used as a security feature. The opticalstructure 10 comprises at least two metal layers 13 and 15. The at leasttwo metal layers 13 and 15 can comprise metals having a ratio of thereal part (n) of the refractive index to the imaginary part (k) of therefractive index (k) that is less than 1. For example, the at least twometal layers 13 and 15 can comprise metals that have an n/k valuebetween about 0.01 and about 0.6, between about 0.015 and about 0.6,between about 0.01 and about 0.5, between about 0.01 and about 0.2,between about 0.01 and about 0.1, or any value in a range or sub-rangedefined by these values. Accordingly, the at least two metal layers 13and 15 can comprise silver, silver alloys, gold, aluminum or copper andtheir respective alloys. Nickel (Ni) and Palladium (Pd) can be used insome implementations. In some cases, however, the at least two metallayers 13 and 15 do not comprise chromium, titanium, and/or tungsten orany metal having an n/k ratio greater than 0.6. In some cases, the metallayer 13 and 15 can have a thickness greater than or equal to about 3 nmand less than or equal to about 35 nm. For example, thickness of themetal layer 13 and 15 can be greater than or equal to about 10 nm andless than or equal to about 30 nm, greater than or equal to about 15 nmand less than or equal to about 27 nm, greater than or equal to about 20nm and less than or equal to about 25 nm, or any value in a range orsub-range defined by these values. The thickness of the metal layer 13can be equal to the thickness of the metal layer 15. Alternately, thethickness of the metal layer 13 can be greater than or less than thethickness of the metal layer 15.

A transparent dielectric layer 14 is sandwiched between the at least twometal layers 13 and 15. The dielectric layer 14 can have a refractiveindex greater than, less than or equal to 1.65. Materials with an indexgreater than or equal to 1.65 can be considered as high refractive indexmaterials for the purpose of this application and materials with anindex less than 1.65 can be considered as low index materials for thepurpose of this application. The transparent dielectric layer 14 cancomprise inorganic materials including but not limited to silicondioxide (SiO₂), aluminum oxide (Al₂O₃), magnesium fluoride (MgF₂),cerium fluoride (CeF₃), lanthanum fluoride (LaF₃), zinc oxide (ZnO),zinc sulfide (ZnS), zirconium dioxide (ZrO₂), titanium dioxide (TiO₂),tantalum pentoxide (Ta₂O₅), ceric oxide (CeO₂), yttrium oxide (Y₂O₃),indium oxide (In₂O₃), tin oxide (SnO₂), indium tin oxide (ITO) andtungsten trioxide (WO₃) or combinations thereof. The transparentdielectric layer 14 can comprise polymers including but not limited toparylene, acrylates, and/or methacrylate. Without any loss ofgenerality, the transparent dielectric layer 14 can comprise a materialhaving an index of refraction greater than, less than, or equal to 1.65and an extinction coefficient between 0 and about 0.5 such that it haslow absorption of light in the visible spectral range.

The dielectric layer 14 can have a thickness that is greater than orequal to about 75 nm and less than or equal to about 2 micron. Forexample, the dielectric layer 14 can have a thickness that is greaterthan or equal to about 150 nm and less than or equal to about 650 nm,greater than or equal to about 200 nm and less than or equal to about600 nm, greater than or equal to about 250 nm and less than or equal toabout 550 nm, greater than or equal to about 300 nm and less than orequal to about 500 nm, greater than or equal to about 350 nm and lessthan or equal to about 450 nm, greater than or equal to about 700 nm andless than or equal to about 1 micron, greater than or equal to about 900nm and less than or equal to about 1.1 micron, greater than or equal toabout 1 micron and less than or equal to about 1.2 micron, greater thanor equal to about 1.2 micron and less than or equal to about 2.0 micronsor any value in a range/sub-range defined by these values. Withoutsubscribing to any particular theory, in various implementations, thethickness of the dielectric layer 14 can be approximately a quarterwavelength of light (e.g., visible light) incident thereon or an integermultiple of a quarter wavelength. In various implementations, thethickness of the dielectric layer 14 may be, for example, ¼, ¾, 5/4,7/4, 9/4, 10/4, etc. of the wavelength of visible light incident on thedielectric layer 14.

The optical structure 10 further comprises a transparent dielectriclayer 12 that is disposed on a side of the metal layer 13 that isopposite to the dielectric layer 14 and a transparent dielectric layer16 that is disposed on a side of the metal layer 15 that is opposite tothe dielectric layer 14. In some cases, layers 12 and 16 can comprisematerials having a refractive index greater than or equal to 1.65. Forexample, layers 12 and 16 can comprise ZrO₂, TiO₂, ZnS, ITO (indium tinoxide), CeO₂ or Ta₂O₃. Dielectric layers 12 and 16 can have a thicknessthat is greater than or equal to about 100 nm and less than or equal toabout 400 nm, greater than or equal to about 150 nm and less than orequal to about 350 nm, greater than or equal to about 200 nm and lessthan or equal to about 300 nm, or any value in a range/sub-range definedby these values. The thickness of the dielectric layer 12 can be equalto the thickness of the dielectric layer 16. Alternately, the thicknessof the dielectric layer 12 can be greater than or less than thethickness of the dielectric layer 16. The optical structure 10 can havea thickness that is less than or equal to about 2 microns.

Fabricating the optical structure 10 can include providing the layer ofdielectric material 12 (or the layer of dielectric material 16) anddepositing the metal layer 13 (or the metal layer 15) over the layer ofdielectric material 12 (or the layer of dielectric material 16). Themetal layer 13 (or the metal layer 15) can be deposited over the layerof dielectric material 12 (or the layer of dielectric material 16) usingan electroless method discussed in further detail below. The metal layer13 (or the metal layer 15) can be deposited as a continuous thin film,as small spheres, metallic clusters or island like structures. The otherdielectric layer 14 can be subsequently disposed over the metal layer 13(or the metal layer 15). The initial layer of dielectric material 12 (orthe layer of dielectric material 16) can be disposed and/or formed overa support. The support is also referred to herein as a base layer. Thesupport can comprise a carrier. The support can comprise a sheet such asa web. The support can comprise a substrate. The substrate can be acontinuous sheet of PET or other polymeric web structure. The supportcan comprise a non-woven fabric. Non-woven fabrics can be flat, poroussheets comprising fibers. In some implementations, the non-woven fabriccan be configured as a sheet or a web structure that is bonded togetherby entangling fiber or filaments mechanically, thermally, or chemically.In some implementations, the non-woven fabric can comprise perforatedfilms (e.g., plastic or molten plastic films). In some implementations,the non-woven fabric can comprise synthetic fibers such as polypropyleneor polyester or fiber glass.

The support can be coated with a release layer comprising a releaseagent. The release agent can be soluble in solvent or water. The releaselayer can be polyvinyl alcohol, which is water soluble or an acrylatewhich is soluble in a solvent. The release layer can comprise a coating,such as, for example, salt (NaCl) or cryolite (Na₃AlF₆) deposited byevaporation before the layers of the optical structure aredeposited/formed.

In some implementations of the support configured as a non-woven fabric,the non-woven fabric can be coated with a release layer. Suchimplementations can be dipped or immersed in a solvent or water thatacts as a release agent to dissolve or remove the release layer. Therelease agent (e.g., the solvent or water) is configured to penetratefrom a side of the non-woven fabric opposite the side on which theoptical structure is disposed to facilitate release of the opticalstructure instead of having to penetrate through the optical structure.The optical structure is recovered from the solvent or water afterdissolution of the release layer. In some manufacturing approaches, therecovered optical structure can then be processed into a pigment.

In one method of fabrication, the optical structure 10 can befabricated, for example, deposited or formed on a coated web, a coatedbase layer, a coated carrier or a coated substrate. The coating on theweb, the base layer, the substrate or the carrier can be configured as arelease layer to facilitate easy removal of the optical structure 10.

The optical structure 10 can be configured as a film or a foil bydisposing over a substrate or other support layer having a thickness,for example, greater than or equal to about 10 microns and less than orequal to about 25 microns. For example, a substrate or support layersuch as a polyester substrate or support layer can have a thicknessgreater than or equal to 12 microns and less than or equal to 22.5microns, greater than or equal to 15 microns and less than or equal toabout 20 microns. The substrate or support layer can comprise materials,such as, for example, polyethylene terphthalate (PET), acrylate,polyester, polyethylene, polypropylene, or polycarbonate. The support orsupport layer itself can be dissolvable. The support or support layer,for example, can also comprise polyvinyl alcohol, which can bedissolved, for example, in water. Accordingly, instead of using arelease layer on a insoluble support web, the support web itself maycomprise soluble material. Accordingly, the support or support layer canbe dissolved leaving the optical coating remaining. The opticalstructure 10 configured as a film or a foil can be encapsulated with apolymer, such as, for example a UV cured polymer.

The optical structure 10 can comprises additional layers. For example, athin protective layer may be disposed between the metal layer 13 and thedielectric layer 12 and/or between the metal layer 15 and the dielectriclayer 16. The protective layer can comprise materials, such as, forexample, NiCrO_(x), Si₃N₄, CeSnO₄ and ZnSnO₄. The protective layers canhave a thickness between about 3-5 nm. The protective layers canadvantageously increase the durability of the metal layers 13 and 15.

Instead of a film, the optical structure, 10, may be removed from thesubstrate, web, carrier, or support layer on which it is fabricated anddivided into platelets having a size that is suitable for a pigment orprinting ink. Platelets having a size that is suitable for a pigment orprinting ink can have an area, length, and/or width that is about 5-10times the thickness of the platelet, in some implementations.Accordingly, the platelets having a thickness of about 1 micron, and/orcan have a width and/or a length that is between approximately 5 micronand about 50 microns. For example, the width and/or a length can begreater than or equal to about 5 micron and less than or equal to about15 microns, greater than or equal to about 5 microns and less than orequal to about 10 microns, greater than or equal to about 5 micron andless than or equal to about 40 microns, greater than or equal to about 5microns and less than or equal to about 20 microns, or any value in theranges/sub-ranges defined by these values. Platelets having a lengthand/or width that is less than about 5-10 times the thickness of theplatelet, such as, for example having a length and/or width that isequal to the thickness of the platelet can be oriented along their edgesin the printing ink or pigment. This can be disadvantageous sincepigment or printing ink comprising platelets that are oriented alongtheir edges may not exhibit the desired colors in reflection andtransmission modes. Dimensions such as, thicknesses, lengths and/orwidths outside these ranges are also possible.

FIG. 12A-1 illustrates an example of a platelet 20. The opticalstructure, 10 is fractured, cut, diced or otherwise separated to obtainthe separate, for example, microns sized, pieces or platelets. In someimplementations, the obtained platelets may be surrounded by anencapsulating layer 21. The encapsulating layer 21 can comprise amoisture resistant material, such as, for example silicon dioxide. Theencapsulating layer 21 can also comprise silica spheres 22 and 23. Thesilica spheres 22 and 23 can be of the same size or have differentsizes. The encapsulating layer 21 can help protect the at least twometal layers 13 and 15 from corrosion. The encapsulating layer 21 canadditionally and/or alternatively reduce the occurrence of delaminationof the at least two metal layers 13 and 15 from the other layers of theoptical structure 10. The optical structures 10 surrounded by theencapsulating layer 21, and potentially comprising the silica spheres 22and 23, can be configured as platelets 20 that are suitable for apigment or printing ink. The silica spheres 22 and 23 of theencapsulating layer 21 can help prevent the platelets from adhering toone another. Without the spheres the platelets may stick together liketwo microscope slides stick together. The spheres 22 and 23 can alsoprevent the platelets 20 from sticking to the print rollers in theprinting machine. One method of surrounding the optical structure 10with an encapsulating layer 21 can rely on sol-gel technology usingtetraethylorthosilicate (TEOS). In one method of forming theencapsulating layer 21, an alcohol based solution of TEOS can be addedin small quantities (e.g., one or more drops at a time) to a dispersionof the platelets in alcohol or water. A catalyst, such as, for example,an acid or sodium hydroxide solution can be added into the a dispersionof the platelets in alcohol or water in small quantities (e.g., one ormore drops at a time). The dispersion of the platelets in alcohol orwater can be heated to a temperature of about 50-70° C., while stirringto transform TEOS to a silica coating. Other processes, however, may beemployed.

In some embodiments, a plurality of platelets 20 can form a pigment.Such a pigment may be color shifting (e.g., the color reflected and/ortransmitted changes with angle of view or angle of incidence of light),in some cases. In some embodiments, non-color shifting pigment or dyemay be mixed with the pigment. In some embodiments other materials maybe included with the platelets 20 to form the pigment. Although some ofthe pigments discussed herein can provide color shift with change inviewing angle or angle of incidence of light, pigments that do notexhibit color shift with change in viewing angle or angle of incidenceof light or that produce very little color shift with change in viewingangle or angle of incidence of light are also contemplated.

In some embodiments, the platelets 20 can be added to a medium such as apolymer 25 (e.g., a polymeric resin) to form a dichroic ink, a pigment,or paint as shown in FIG. 12B-1. The platelets can be suspended in themedium (e.g., polymer) 25. The platelets can be randomly oriented in themedium (e.g., polymer) 25 as shown in FIG. 12B-1. During the printingprocess, in some cases, the individual platelets can be orientedparallel to the surface of the object (e.g., paper) to which thepigment, the paint, or the dichroic ink is being applied as a result of,for example, the printing action, gravity, and/or surface tension of thenormal drying process of the pigment, the paint, or the dichroic ink asshown in FIG. 12B-2. The medium 25 can comprise material including butnot limited to acrylic melamine, urethanes, polyesters, vinyl resins,acrylates, methacrylate, ABS resins, epoxies, styrenes and formulationsbased on alkyd resins and mixtures thereof. In some implementations, themedium 25, e.g., polymer, can have a refractive index that closelymatches the refractive index of the encapsulating silica layer 21 and/orsilica balls such that the encapsulating layer and/or the silica ballsdo not adversely affect the optical performance of the pigment, thepaint, or the dichroic ink in the medium.

In various implementations, the platelets 20 need not be surrounded byan encapsulating layer. In such implementations, one or more platelets20 that are not encapsulated by an encapsulating layer can be added ormixed with an ink or a pigment medium (e.g., varnish, polymeric resin,etc.) to obtain a dichroic ink or pigment as discussed above. In variousimplementations, the dichroic ink or pigment can comprise a plurality ofplatelets 20. The optical structures 10 that are configured as theplurality of platelets 20 can have different distributions of shapes,sizes, thicknesses and/or aspect ratios. The optical structures 10 thatare configured as the plurality of platelets 20 can also have differentoptical properties. For example, the optical structures 10 that areconfigured as the plurality of platelets 20 can also have differentcolor properties.

In some implementations, an optical structure comprising only the metallayers 13 and 15 and the transparent dielectric layer 14 without thehigh refractive index dielectric layers 12 and 16 as depicted in FIG.12A-2 can be configured as platelets as discussed above and dispersed inthe medium 25 as shown in FIG. 12B-2 to manufacture a dichroic printingink, paint or pigment as discussed above. In some implementations, theplatelets including an optical structure comprising only the metallayers 13 and 15 and the transparent dielectric layer 14 without thehigh refractive index dielectric layers 12 and 16 need not beencapsulated in an encapsulating layer as discussed above.

A silane coupling agent can be bonded to the encapsulating layer 21 toform a functionalized platelet 30 as shown in FIG. 13. Bonding of thesilane coupling agent to the encapsulating layer can occur through ahydrolyzing reaction. The silane coupling agent can bind to the polymer(e.g., polymeric resin) of the printing ink or paint medium so that theheterogeneous mixture of pigment and the polymer do not separate duringthe printing process and substantially function in much the same way asa homogeneous medium would function. The printing ink or paint mediumcan comprise material including but not limited to acrylic melamine,urethanes, polyesters, vinyl resins, acrylates, methacrylate, ABSresins, epoxies, styrenes and formulations based on alkyd resins andmixtures thereof. The silane coupling agents used can be similar to thesilane coupling agents sold by Gelest Company (Morristown, Pa. USA). Insome implementations, the silane coupling agent can comprise ahydrolyzable group, such as, for example, an alkoxy, an acyloxy, ahalogen or an amine. Following a hydrolyzing reaction (e.g.,hydrolysis), a reactive silanol group is formed, which can condense withother silanol groups, for example, with the silica spheres of theencapsulating layer 21 or the encapsulating layer of silica to formsiloxane linkages. The other end of the silane coupling agent comprisesthe R-group 31. The R-group 31 can comprise various reactive compoundsincluding but not limited to compounds with double bonds, isocyanate oramino acid moieties. Reaction of the double bond via free radicalchemistry can form bonds with the ink polymer(s) such as those based onacrylates, methacrylates or polyesters based resins. For example,isocyanate functional silanes, alkanolamine functional silanes andaminosilanes can form urethane linkages.

Without any loss of generality, in various implementations of theoptical structure 10 configured as a platelet that do not comprise theencapsulating layer, the silane coupling agent can be bonded to one orboth of the high refractive index dielectric layers 12 and 16 comprisinga dielectric material (e.g., TiO₂) suitable to be bonded with the silanecoupling agent.

Without any loss of generality, the optical structure 10 can beconsidered as an interference stack or cavity. Ambient light incident onthe surface of the optical structure 10 is partially reflected from thevarious layers of the optical structure 10 as shown by rays 47 and 48 inFIG. 14 and partially transmitted through the various layers of theoptical structure 10 as shown by ray 49 in FIG. 14. FIG. 14 illustratesan embodiment of an optical structure 10 comprising the high refractiveindex dielectric layer 12 and 16, metal layers 13 and 15 and adielectric layer 14 encapsulated in the encapsulating layer 21. Somewavelengths of the ambient light reflected from the various layers mayinterfere constructively and some other wavelengths of the ambient lightreflected from the various layers may interfere destructively.Similarly, some wavelengths of light transmitted through the variouslayers may interfere constructively and some other wavelengths of theambient light transmitted through the various layers may interferedestructively. As a result of which, the optical structure 10 appearscolored when viewed in transmission and reflection mode. In general, thecolor and the intensity of light reflected by and transmitted throughthe optical structure 10 can depend on the thickness and the material ofthe various layers of the optical structure 10. By changing the materialand the thickness of the various layers, the color and intensity oflight reflected by and transmitted through the optical structure 10 canbe varied. Without subscribing to any particular scientific theory aboutthe operation of the optical structures 10, in general, the material andthe thickness of the various layers can be configured such that some orall of the ambient light reflected by the various layers interfere suchthat a node 45 in the field 42 occurs at the two metal layer 13 and 15.Without subscribing to any particular scientific theory, it is notedthat in some cases those wavelengths that are substantially equal to thethickness of the spacer layer (e.g., wavelengths within about ±10% ofthe thickness of the spacer layer) will interfere such that a node 45 inthe field 42 occurs at the two metal layer 13 and 15. For otherwavelengths, a node 45 might not occur. Accordingly, in someimplementations, the two metal layers 13 and 15 might not be visible inthe reflection mode. Again, without subscribing to a particularscientific theory, based on the thickness of the two metal layers 13 and15 and the transparent dielectric layer 14, a portion of the incidentlight may be transmitted through the optical structure 10 as a result ofthe phenomenon of “induced transmittance” or “induced transmission”. Thereflection and transmission spectral characteristics are discussedbelow.

FIG. 15A shows a spectral plot in both transmission (curve 501 a) andreflection (curve 503 a) for a first example of the optical structure10. The materials of the various layers of the first example of theoptical structure 10 and the thickness of the various layers of thefirst example of the optical structure 10 are provided in Table 1 below.As indicated in Table 1, the first example of the optical structure 10comprises two metal layers comprising silver. The two silver layerscorrespond to the at least two metal layer 13 and 15 of the opticalstructure 10 shown in FIG. 11. Both the silver layers have the samethickness of 25 nm. A dielectric layer having a thickness of 300 nm issandwiched between the two silver layers. The dielectric layer comprisesSiO₂ which has a refractive index of 1.47011. The dielectric layercomprising SiO₂ corresponds to the transparent layer 14 having a lowrefractive index (i.e., refractive index less than 1.65). A layer ofZrO₂ is disposed on the side of each of the two silver layers that isopposite the side facing the SiO₂ layer. Each of the two layerscomprising ZrO₂ has a thickness of 150 nm. As noted from Table 1 below,ZrO₂ has a refractive index of 2.27413. The two layers comprising ZrO₂corresponds to the transparent layers 12 and 16 having a high refractiveindex (i.e., refractive index greater than or equal to 1.65). The firstexample of the optical structure 10 is encapsulated in a SiO₂ matrix asindicated in Table 1. The SiO₂ matrix is used to simulate the printingmedium or ink which has a similar refractive index.

The transmission and reflection of light observed at an angle of 0degrees with respect to a normal to the first example of the opticalstructure 10 is shown in FIG. 15A. The reflection spectrum 503 a(indicated as curve #1 in FIG. 15A) and the transmission spectrum 501 a(indicated as curve #0 in FIG. 15A) in the spectral range between about400 nm and about 700 nm which includes the visible spectral range wereobtained using a simulation software from http://thinfilm.hansteen.net.

TABLE 1 Parameters of a first example of the optical structure that hasthe reflection and transmission spectra as shown in FIG. 15A. ParametersCurve #0 # # Slab: # SIO2 N = (1.47011, 0) mynkdb/SIO2.NK # ZRO2 d =1.5e−07 N = (2.27413, 0) mynkdb/ZRO2.NK # AG d-2.5e−08 N = (0.173038,1.94942) mynkdb/AG.NK # SIO2 d = 3e−07 N = (1.47011, 0) mynkdb/SIO2.NK #AG d = 2.5e−08 N = (0.173038, 1.94942) mynkdb/AG.NK # ZRO2 d = 1.5e−07 N= (2.27413, 0) mynkdb/ZRO2.NK # SIO2 N = (1.47011, 0) mynkdb/SIO2.NK # #Beam: # Wavelength = (4e−07, 0) Angle = 0.0174533 Polarization = 1 N =(1.47011, 0) # # Supported spectral range: 2.5e−07 m-8.5e−07 m. # #Lambda[nm] R[ ] # Curve #1 # # Slab: # SIO2 N = (1.47011, 0)mynkdb/SIO2.NK # ZRO2 d = 1.5e−07 N = (2.27413, 0) mynkdb/ZRO2.NK # AG d= 2.5e−08 N = (0.173038, 1.94942) mynkdb/AG.NK # SIO2 d = 3e−07 N =(1.47011, 0) mynkdb/SIO2.NK # AG d = 2.5e−08 N = (0.173038, 1.94942)mynkdb/AG.NK # ZRO2 d = 1.5e−07 N = (2.27413, 0) mynkdb/ZRO2.NK # SIO2 N= (1.47011, 0) mynkdb/SIO2.NK # # Beam: # Wavelength = (4e−07, 0) Angle= 0.0174533 Polarization = 1 N = (1.47011, 0) # # Supported spectralrange: 2.5e−07 m-8.5e−07 m. # # Lambda[nm] T[ ] #

It can be seen from FIG. 15A that the transmission curve 501 a (curve#0) has a peak with a maximum value occurring at a wavelength of about520 nm and the reflection curve 503 a has two peaks with a first maximumvalue occurring at a wavelength of 420 nm and a second maximum valueoccurring at a wavelength of about 650 nm. The maximum value of thetransmission and reflection peaks is greater than 0.5 which indicatesthat the transmission and reflection peaks have high intensities.Furthermore, the transmission and reflection peaks have a bandwidth asmeasured at 50% of the maximum value of the peak greater than about 20nm. The bandwidth as measured at 50% of the maximum value of the peak isreferred to as full width at half maximum (FWHM). It is observed fromFIG. 15A that the FWHM of the transmission peak is about 75 nm.

Based on the position of the transmission and reflection peaks and thebandwidth of the transmission and reflection peaks, the opticalstructure 10 can be perceived as having a first color in the reflectionmode and a second color in the transmission mode by an average humaneye. In some cases, the first color and the second color can becomplimentary colors. In some cases, the transmission and reflectionpeaks comprising a range of wavelengths of the visible spectral rangecan have a high intensity and a FWHM greater than 2 nm (e.g., FWHMgreater than or equal to about 10 nm, FWHM greater than or equal toabout 20 nm, FWHM greater than or equal to about 30 nm, FWHM greaterthan or equal to about 40 nm, FWHM greater than or equal to about 50 nm,FWHM greater than or equal to about 60 nm, FWHM greater than or equal toabout 70 nm, FWHM greater than or equal to about 100 nm, FWHM greaterthan or equal to about 200 nm, FWHM less than or equal to about 300 nm,FWHM less than or equal to about 250 nm, or any value in arange/sub-range defined by these values).

The one or more reflection peaks can be considered to have a highintensity if the reflectivity or reflectance of the peak in a range ofvisible wavelengths is greater than or equal to about 50% and less thanor equal to about 100%. For example, the one or more reflection peakscan be considered to have a high intensity if the amount of lightreflected or reflectivity or reflectance in a range of visiblewavelengths is greater than or equal to about 55% and less than or equalto about 99%, greater than or equal to about 60% and less than or equalto about 95%, greater than or equal to about 70% and less than or equalto about 90%, greater than or equal to about 75% and less than or equalto about 85%, or any value in a range/sub-range defined by these values.

The one or more transmission peaks can be considered to have a highintensity if the transmissivity or transmittance of the peak in a rangeof visible wavelengths is greater than or equal to about 50% and lessthan or equal to about 100%. For example, the one or more transmissionpeaks can be considered to have a high intensity if the amount of lighttransmitted or transmissivity or transmittance in a range of visiblewavelengths is greater than or equal to about 55% and less than or equalto about 99%, greater than or equal to about 60% and less than or equalto about 95%, greater than or equal to about 70% and less than or equalto about 90%, greater than or equal to about 75% and less than or equalto about 85%, or any value in a range/sub-range defined by these values.

The first example of the optical structure 10 having a design asdepicted in Table 1 and having a reflection spectrum and a transmissionspectrum as shown in FIG. 15A appears green in transmission mode and asmagenta in reflection mode to an average human eye. Without any loss ofgenerality, it can be advantageous, in various implementations, for thepeaks in the reflection and transmission spectra to be non-overlappingas shown in FIGS. 15A and 15B such that a reflection peak having ahighest possible reflectance or reflectivity can be obtained in oneregion of the visible spectral range and a transmission peak having ahighest possible transmittance or transmissivity can be obtained in anon-overlapping region of the visible spectral range. Accordingly, thereflected color and the transmitted color can be different andpotentially complementary to each other, such as, for example, red andgreen, yellow and violet, blue and orange, green and magenta, etc.

The shape of the transmission and reflection peaks, the position of themaximum of the transmission and reflection peaks, the FWHM of thetransmission and reflection peaks, etc. can be varied by varying thematerials and/or thickness of the various layers of the opticalstructure 10. This can be observed from FIG. 15B which depicts thereflection spectrum 503 b and transmission spectrum 501 b of a secondexample of the optical structure 10 which has the same materialcomposition as the first example of the optical structure 10 butdifferent thickness for the various layers. The parameters of the secondexample of the optical structure 10 are provided in Table 2 below. Asnoted from Table 2, the thickness of the dielectric layer comprisingSiO₂ and having a refractive index of 1.47011 in the second example ofthe optical structure 10 is 400 nm instead of 300 nm in the firstexample of the optical structure 10. Furthermore, the thickness of thetwo ZrO₂ disposed on either side of each of the two silver layers is 225nm in the second example of the optical structure 10 instead of 150 nmin the first example of the optical structure 10.

TABLE 2 Parameters of a second example of the optical structure that hasthe reflection and transmission spectra as shown in FIG. 15B. ParametersCurve #0 # # Slab: # SIO2 N = (1.47011, 0) mynkdb/SIO2.NK # ZRO2 d =2.25e−07 N = (2.27413, 0) mynkdb/ZRO2.NK # AG d = 2.5e−08 N = (0.173038,1.94942) mynkdb/AG.NK # SIO2 d = 4e−07 N = (1.47011, 0) mynkdb/SIO2.NK #AG d = 2.5e−08 N = (0.173038, 1.94942) mynkdb/AG.NK # ZRO2 d = 2.25e−07N = (2.27413, 0) mynkdb/ZRO2.NK # SIO2 N = (1.47011, 0) mynkdb/SIO2.NK ## Beam: # Wavelength = (4e−07, 0) Angle = 0.0174533 Polarization = 1 N =(1.47011, 0) # # Supported spectral range: 2.5e−07 m-8.5e−07 m. # #Lambda[nm] R[ ] # Curve #1 # # Slab: # SIO2 N = (1.47011, 0)mynkdb/SIO2.NK # ZRO2 d = 2.25e−07 N = (2.27413, 0) mynkdb/ZRO2.NK # AGd = 2.5e−08 N = (0.173038, 1.94942) mynkdb/AG.NK # SIO2 d = 4e−07 N =(1.47011, 0) mynkdb/SIO2.NK # AG d = 2.5e−08 N = (0.173038, 1.94942)mynkdb/AG.NK # ZRO2 d = 2.25e−07 N = (2.27413, 0) mynkdb/ZRO2.NK # SIO2N = (1.47011, 0) mynkdb/SIO2.NK # # Beam: # Wavelength = (4e−07, 0)Angle = 0.0174533 Polarization = 1 N = (1.47011, 0) # # Supportedspectral range: 2.5e−07 m-8.5e−07m. # # Lambda[nm] T[ ] #

As a result of the change in the thickness of the dielectric layerscomprising SiO₂ and ZrO₂ between the second example of the opticalstructure and the first example of the optical structure, an average eyewould perceive the second example of the optical structure to appeargreen in reflection mode and a magenta in transmission mode when viewedalong a direction normal to the surface of the second example of theoptical structure.

The color of the first example and the second example of the opticalstructure 10 as perceived by the average human eye in reflection modeand transmission mode can shift from the above described magenta andgreen colors at different viewing angles with respect to the normal tothe surface of the first example and the second example of the opticalstructure 10. For example, the first example of the optical structure 10can appear yellowish green in reflection mode and blue in transmissionmode when viewed at an angle of about 35 degrees with respect to thenormal to the surface of the first example of the optical structure 10.As another example, the second example of the optical structure 10 canappear pale purple in reflection mode and yellowish in transmission modewhen viewed at an angle of about 35 degrees with respect to the normalto the surface of the second example of the optical structure 10.Without any loss of generality, the reflection and the transmissionpeaks can exhibit a blue shift towards shorter wavelengths as theviewing angle with respect to the normal to the surface of the firstexample and the second example of the optical structure 10 increases.

TABLE 3 CIELab values for transmission mode when the first example ofthe optical structure having parameters as described in Table 1 isviewed at different viewing angles in the presence of a D65 lightsource. Incident Angle L* a* b* 0.0 66.0433 −91.9989 11.4335 Design:First Example of 5.0 65.5578 −91.5328 9.3070 the Optical Structure 10.064.0035 −89.0283 2.6936 Polarization: P 15.0 61.1497 −81.1844 −8.9303Source: D65 20.0 56.8304 −63.3282 −25.7758 Observer: CIE 1931 25.051.2146 −32.8229 −46.6651 Mode: Transmittance 30.0 44.8902 5.7777−67.7337 35.0 38.6590 39.5335 −81.9630 40.0 33.4474 53.5162 −81.665245.0 30.4059 43.0007 −64.1869

TABLE 4 CIELab values for reflection mode when the first example of theoptical structure having parameters as described in Table 1 is viewed atdifferent viewing angles in the presence of a D65 light source. IncidentAngle L* a* b* 0.0 79.2753 51.6407 −11.0765 Design: First Example of 5.079.6541 50.6966 −9.6957 the Optical Structure 10.0 80.8290 47.4222−5.3025 Polarisation: P 15.0 82.8379 40.8204 2.7687 Source: D65 20.085.5358 30.2258 15.3945 Observer: CIE 1931 25.0 88.5026 16.2157 33.3659Mode: Reflectance 30.0 91.2316 1.0176 55.5312 35.0 93.4068 −11.016970.1468 40.0 94.9289 −14.7597 57.7563 45.0 95.7892 −10.6419 32.4479

Tables 3 and 4 above provide the CIELa*b* values for transmission modeand reflection mode respectively when the first example of the opticalstructure having parameters as described in Table 1 is viewed atdifferent viewing angles in the presence of a D65 light source. Tables 5and 6 below provide the CIELa*b* values for transmission mode andreflection mode respectively when the second example of the opticalstructure having parameters as described in Table 2 is viewed atdifferent viewing angles in the presence of a D65 light source. TheCIELab color closely represent the colors perceived by an average humaneye. The CIELab color space mathematically describe various colorsperceived by an average human eye in the three dimensions L forlightness, a for the color component green-red, and b for the colorcomponent from blue-yellow. The a-axis extends longitudinally in a planefrom green (represented by −a) to red (represented by +a). The b-axisextends along a transverse direction in the plane perpendicular to thea-axis from blue (represented by −b) to yellow (represented by +b). Thebrightness is represented by the L-axis which is perpendicular to thea-b plane. The brightness increases from black represented by L=0 towhite represented by L=100. The CIELab values for different viewingangles using a D65 illuminant were calculated using Essential MacleodThin Film Software.

TABLE 5 CIELab values for transmission mode when the second example ofthe optical structure having parameters as described in Table 2 isviewed at different viewing angles in the presence of a D65 lightsource. Incident Angle L* a* b* 0.0 35.3624 87.7761 −73.0966 Design:Second Example of 5.0 35.9375 88.1214 −71.4170 the Optical Structure10.0 37.8504 88.3232 −65.5105 Polarization: P 15.0 41.5481 86.2320−53.1339 Source: D65 20.0 47.3489 79.0290 −32.0276 Observer: CIE 193125.0 54.8227 62.6584 −2.6495 Mode: Transmittance 30.0 62.6567 31.673029.2861 35.0 68.8117 −13.6155 53.1104 40.0 70.1939 −60.8762 56.3246 45.063.8734 −83.2865 29.4710

TABLE 6 CIELab values for reflection mode when the second example of theoptical structure having parameters as described in Table 2 is viewed atdifferent viewing angles in the presence of a D65 light source. IncidentAngle L* a* b* 0.0 95.0631 −31.7647 48.4548 Design: Second Example of5.0 94.9402 −32.7902 47.4892 the Optical Structure 10.0 94.5010 −35.811843.8268 Polarisation: P 15.0 93.5195 −40.5801 35.7606 Source: D65 20.091.6012 −45.9635 22.4005 Observer: CIE 1931 25.0 88.3120 −46.8681 5.3389Mode: Reflectance 30.0 83.5384 −31.2961 −12.0407 35.0 78.2978 5.6475−26.1375 40.0 76.3297 41.2278 −30.5320 45.0 81.1875 43.5513 −17.6926

The optical performance of two additional examples of optical structureshaving parameters provided in Tables 7 and 8 were analyzed. Theadditional examples of optical structures were designed using EssentialMacleod Thin Film Software. The material composition and the thicknessof the various layers for the third example of the optical structure areprovided in Table 7 and the material composition and the thickness ofthe various layers for the fourth example of the optical structure areprovided in Table 8.

TABLE 7 Material Composition and thickness of the various layers of thethird example of the optical structure 10. Optical Physical Thickness(Full Refractive Extinction Wavelength Optical Thickness Layer MaterialIndex Coefficient Thickness) (nm) SiO2 1.46180 0.00000 1 ZrO2 1.000002.06577 0.00004 1.00000000 246.88 2 Ag 1.00000 0.05100 2.960000.00250000 25.00 3 SiO2 1.00000 1.46180 0.00000 0.50000000 174.44 4 Ag1.00000 0.05100 2.96000 0.00250000 25.00 5 ZrO2 1.00000 2.06577 0.000041.00000000 246.88 Substrate Glass 1.52083 0.00000 Total Thickness2.50500000 718.21

TABLE 8 Material Composition and thickness of the various layers of thefourth example of the optical structure 10. Optical Physical Thickness(Full Refractive Extinction Wavelength Optical Thickness Medium MaterialIndex Coefficient Thickness) (nm) SiO2 1.46180 0.00000 1 ZrO2 1.000002.06577 0.00004 0.50000000 123.44 2 Ag 1.00000 0.05100 2.960000.00250000 25.00 3 SiO2 1.00000 1.46180 0.00000 0.75000000 261.66 4 Ag1.00000 0.05100 2.96000 0.00250000 25.00 5 ZrO2 1.00000 2.06577 0.000040.50000000 123.44 Substrate Glass 1.52083 0.00000 Total Thickness1.75500000 558.55

The material composition of the various layers of the third and thefourth example of the optical structure 10 is the same as the materialcomposition of the various layers of the first and the second example ofthe optical structure 10. For example, similar to the first and thesecond example of the optical structure 10, the third and the fourthexamples of the optical structure 10 comprise a SiO₂ layer sandwiched bytwo silver layers with ZrO₂ layers disposed on the side of the twosilver layers opposite the side facing the SiO₂ layer. However, thethickness of the various layers is different for each of the first,second, third and fourth examples of the optical structure 10.

The third example of the optical structure 10 comprises two silverlayers having a thickness of 25 nm each sandwiching a dielectric layerhaving a thickness of 174.44 nm and comprising SiO₂. The third exampleof the optical structure 10 comprises a layer of ZrO₂ on the side of thesilver layers opposite the side facing the SiO₂ layer. Each ZrO₂ layerhas a thickness of 246.88 nm. The total thickness of the third exampleof the optical structure 10 is 718.21 nm.

The fourth example of the optical structure 10 comprises two silverlayers having a thickness of 25 nm each sandwiching a dielectric layerhaving a thickness of 261.66 nm and comprising SiO₂. The fourth exampleof the optical structure 10 comprises a layer of ZrO₂ on the side of thesilver layers opposite the side facing the SiO₂ layer. Each ZrO₂ layerhas a thickness of 123.44 nm. The total thickness of the fourth exampleof the optical structure 10 is 558.55 nm.

FIG. 16A illustrates the a*b* values in the CIELa*b* color space for thefirst example of the optical structure 10 having parameters as describedin Table 1 for different viewing angles between 0 degrees and 45 degreeswith respect to the normal to the surface of the first example of theoptical structure 10 in reflection mode. It is observed from FIG. 16Athat at a viewing angle of 0 degrees with respect to the normal to thesurface of the first example of the optical structure 10, the firstexample of the optical structure 10 appears magenta to an average humaneye in reflection mode. As the viewing angle increases the colorreflected by the first example of the optical structure 10 shifts alongthe curve 601 a in the direction of the arrow towards yellow.

FIG. 16B illustrates the a*b* values in the CIELa*b* color space for thesecond example of the optical structure 10 having parameters asdescribed in Table 2 for different viewing angles between 0 degrees and45 degrees with respect to the normal to the surface of the secondexample of the optical structure 10 in reflection mode. It is observedfrom FIG. 16B that at a viewing angle of 0 degrees with respect to thenormal to the surface of the second example of the optical structure 10,the second example of the optical structure 10 appears yellowish greento an average human eye in reflection mode. As the viewing angleincreases the color reflected by the second example of the opticalstructure 10 shifts along the curve 601 b in the direction of the arrowtowards magenta.

FIG. 16C illustrates the a*b* values in the CIELa*b* color space for thethird example of the optical structure 10 having parameters as describedin Table 7 for different viewing angles between 0 degrees and 45 degreeswith respect to the normal to the surface of the third example of theoptical structure 10 in reflection mode. It is observed from FIG. 16Cthat at a viewing angle of 0 degrees with respect to the normal to thesurface of the third example of the optical structure 10, the thirdexample of the optical structure 10 appears green to an average humaneye in reflection mode. As the viewing angle increases the colorreflected by the third example of the optical structure 10 shifts alongthe curve 601 c in the direction of the arrow towards blue at 35°. Thetransmission color moves from red to orange as the viewing angleincreases to 35°. It is noted that the various reflection andtransmission color curves move counterclockwise in the various a* b*plots of FIGS. 16A-16D and 17A-17D.

FIG. 16D illustrates the a*b* values in the CIELa*b* color space for thefourth example of the optical structure 10 having parameters asdescribed in Table 8 for different viewing angles between 0 degrees and45 degrees with respect to the normal to the surface of the fourthexample of the optical structure 10 in reflection mode. It is observedfrom FIG. 16D that at a viewing angle of 0 degrees with respect to thenormal to the surface of the fourth example of the optical structure 10,the fourth example of the optical structure 10 appears yellow to anaverage human eye in reflection mode. As the viewing angle increases thecolor reflected by the fourth example of the optical structure 10 shiftsalong the curve 601 d in the direction of the arrow towards grey. Intransmission the color seen at zero degrees is blue moving to magenta at35°. This sample is configured as a dichroic film/pigment that has avery small color shift as the angle of view changes.

FIG. 17A illustrates the a*b* values in the CIELa*b* color space for thefirst example of the optical structure 10 having parameters as describedin Table 1 for different viewing angles between 0 degrees and 45 degreeswith respect to the normal to the surface of the first example of theoptical structure 10 in transmission mode. It is observed from FIG. 17Athat at a viewing angle of 0 degrees with respect to the normal to thesurface of the first example of the optical structure 10, the firstexample of the optical structure 10 appears green to an average humaneye in transmission mode. As the viewing angle increases the colortransmitted by the first example of the optical structure 10 shiftsalong the curve 701 a in the direction of the arrow towards violet.

FIG. 17B illustrates the a*b* values in the CIELa*b* color space for thesecond example of the optical structure 10 having parameters asdescribed in Table 2 for different viewing angles between 0 degrees and45 degrees with respect to the normal to the surface of the secondexample of the optical structure 10 in transmission mode. It is observedfrom FIG. 17B that at a viewing angle of 0 degrees with respect to thenormal to the surface of the second example of the optical structure 10,the second example of the optical structure 10 appears purple to anaverage human eye in transmission mode. As the viewing angle increasesthe color reflected by the second example of the optical structure 10shifts along the curve 701 b in the direction of the arrow towardsgreen.

FIG. 17C illustrates the a*b* values in the CIELa*b* color space for thethird example of the optical structure 10 having parameters as describedin Table 7 for different viewing angles between 0 degrees and 45 degreeswith respect to the normal to the surface of the third example of theoptical structure 10 in transmission mode. It is observed from FIG. 17Cthat at a viewing angle of 0 degrees with respect to the normal to thesurface of the third example of the optical structure 10, the thirdexample of the optical structure 10 appears red to an average human eyein transmission mode. As the viewing angle increases the color reflectedby the third example of the optical structure 10 shifts along the curve701 c in the direction of the arrow towards orange.

FIG. 17D illustrates the a*b* values in the CIELa*b* color space for thefourth example of the optical structure 10 having parameters asdescribed in Table 8 for different viewing angles between 0 degrees and45 degrees with respect to the normal to the surface of the fourthexample of the optical structure 10 in transmission mode. It is observedfrom FIG. 17D that at a viewing angle of 0 degrees with respect to thenormal to the surface of the fourth example of the optical structure 10,the fourth example of the optical structure 10 appears blue to anaverage human eye in transmission mode. As the viewing angle increasesthe color reflected by the fourth example of the optical structure 10shifts along the curve 701 d in the direction of the arrow towardsmagenta.

The optical structures 10 are considered to be illuminated by D65illumination for generating the curves of FIGS. 16A-16D and 17A-17D.

FIGS. 18A and 18B respectively illustrate the transmittance andreflectance spectra for the third example of the optical structure 10having parameters as described in Table 7. As noted, from FIGS. 18A and18B, the third example of the optical structure 10 has a peaktransmittance at about 650 nm while the reflectance is substantiallyuniform in the spectral region between about 400 nm and about 600 nm anda dip around 650 nm.

FIGS. 18C and 18D respectively illustrate the transmittance andreflectance spectrum for the fourth example of the optical structure 10having parameters as described in Table 8. As noted, from FIGS. 18C and18D, the fourth example of the optical structure 10 has a peaktransmittance between about 470 nm and about 480 nm while thereflectance is substantially uniform in the spectral region betweenabout 520 nm and about 700 nm and a dip around 470 nm.

The optical performance of an additional fifth example of the opticalstructure 10 are analyzed. The fifth example of the optical structure 10comprised a glass substrate, a first dielectric layer comprising CeO₂over the substrate, a first metal layer comprising aluminum over thefirst dielectric layer, a second dielectric layer comprising CeO₂ overthe first metal layer, a second metal layer comprising aluminum over thesecond dielectric layer, and a third dielectric layer comprising CeO₂over the second metal layer. The thickness of various metal anddielectric layers can be configured to appear blue/violet intransmission at a viewing angle between about 0 degrees and about 40degrees with respect to a normal to the surface of the fifth example ofthe optical structure 10 and yellow/green in reflection at viewingangles between 0 degrees and about 40 degrees with respect to a normalto the surface of the fifth example of the optical structure 10.

FIGS. 18E and 18F respectively illustrate the transmittance andreflectance spectrum for the fifth example of the optical structure 10discussed above. FIG. 18G illustrates the a*b* values in the CIELa*b*color space for the fifth example of the optical structure 10 fordifferent viewing angles between 0 degrees and 40 degrees with respectto the normal to the surface of the fourth example of the opticalstructure 10 in transmission mode. It is observed from FIG. 18G that ata viewing angle of 0 degrees with respect to the normal to the surfaceof the fifth example of the optical structure 10, the fifth example ofthe optical structure 10 appears blue to an average human eye intransmission mode. As the viewing angle increases the color reflected bythe fifth example of the optical structure 10 shifts along the curve 751a in the direction of the arrow towards violet.

FIG. 18H illustrates the a*b* values in the CIELa*b* color space for thefifth example of the optical structure 10 for different viewing anglesbetween 0 degrees and 40 degrees with respect to the normal to thesurface of the fifth example of the optical structure 10 in reflectionmode. It is observed from FIG. 18H that at a viewing angle of 0 degreeswith respect to the normal to the surface of the fifth example of theoptical structure 10, the fifth example of the optical structure 10appears yellow to an average human eye in reflection mode. As theviewing angle increases the color reflected by the fifth example of theoptical structure 10 shifts along the curve 751 b in the direction ofthe arrow towards green.

Various implementations of an optical structure that can be used as asecurity feature can comprise a dielectric region comprising one or moredielectric materials surrounded by a partially optically transmissive orpartially reflective metal layer (e.g., partially reflective andpartially transmissive metal layer). For example, the optical structurecan comprise a dielectric region having first and second major surfaces(e.g., top and bottom) and edges (or sides) therebetween. The partiallyreflective and partially transmissive metal layer can be disposed on theedges (or sides) in addition to being disposed on the first and secondmajor surfaces (e.g., top and bottom). In various implementations, thedielectric region comprising the one or more dielectric materials isoptical transmissive and in some configurations may be opticallytransparent. In certain implementations, the region comprising the oneor more dielectric materials is surrounded by a partially opticallytransmissive and partially reflective metal layer. In variousimplementations, the one or more dielectric materials can comprisepolymer, glass, oxides (e.g., SiO₂, TiO₂) or other dielectric materials.In various implementations, the dielectric region can comprise adielectric substrate coated with a one or more dielectric materials(e.g., layers) having a refractive index equal to, less than or greaterthan the refractive index of the dielectric substrate. In variousimplementations, the dielectric region can comprise a first dielectricmaterial (e.g., first dielectric layer) having a first refractive indexsurrounded by a second dielectric material (e.g., second dielectriclayer) having a second refractive index. The second refractive index canbe equal to, less than or greater than the first refractive index.

FIGS. 19A and 19B illustrate different embodiments of such opticalstructures. FIG. 19A schematically illustrates a cross-sectional view ofan embodiment of an optical structure 70 a comprising a dielectricregion 30 a surrounded by a partially reflective and partiallytransmissive metal layer 35 a. The optical structure 70 a shown in FIG.19A has a rectilinear (e.g., rectangular) cross-section. FIG. 19Bschematically illustrates a cross-sectional view of another embodimentof an optical structure 70 b comprising a dielectric region 30 bsurrounded by a partially reflective and partially transmissive metallayer 35 b. The optical structure 70 b shown in FIG. 19B has a circularcross-section.

The dielectric region 30 a and/or 30 b can comprise one or moredielectric materials such as, for example, polymer, magnesium fluoride,silicon dioxide, aluminum oxide, titanium oxide, cerium oxide, anytransparent oxide material, any transparent nitride material, anytransparent sulfide material, glass, combinations of any of thesematerials or any other inorganic or organic material. The refractiveindex of the one or more dielectric materials in the dielectric region30 a and/or 30 b can have a value between about 1.35 and about 2.5. Forexample, the refractive index of the one or more dielectric materials inthe dielectric region 30 a and/or 30 b can have a value between about1.38 and 1.48, between about 1.48 and about 1.58, between about 1.58 andabout 1.78, between about 1.75 and about 2.0, between about 2.0 andabout 2.25, between about 2.25 and about 2.5, or any value in anyrange/sub-range defined by these values. Values outside these ranges arealso possible, in some implementations. The dielectric region 30 aand/or 30 b can comprise a dielectric substrate coated with a one ormore dielectric materials having a refractive index equal to, less thanor greater than the refractive index of the dielectric substrate. Invarious implementations, the dielectric region 30 a and/or 30 b cancomprise a first dielectric material having a first refractive indexsurrounded by a second dielectric material having a second refractiveindex. The second refractive index can be equal to, less than or greaterthan the first refractive index.

In various implementations, the dielectric region 30 a and/or 30 b canbe configured as a slab, flake, a sphere, spheroid, ellipsoid, disc, orany other 3-dimensional shape enclosing a volume. The dielectric region30 a and/or 30 b may have a regular or irregular shape. For example, asshown in FIG. 19A, the dielectric region 30 a can be configured as aslab having two major surfaces 31 a and 31 b and one or more edgesurfaces disposed between the two major surfaces 31 a and 31 b. In someimplementations, a number of edges surfaces may be disposed between thetwo major surfaces 31 a and 31 b. The number of edge surfaces may, forexample, be one, two, three, four, five, six, seven, eight, nine, ten,twelve, twenty, thirty, fifty, etc. or in any range between any of thesevalues. Values outside these ranges are also possible. The majorsurfaces 31 a and 31 b can have a variety of shapes. For example, one orboth of the major surfaces 31 a and 31 b can have a rectilinear orcurvilinear shape in certain implementations. The shape may be regularor irregular in certain implementations. For example, one or both of themajor surfaces 31 a and 31 b can have a square shape, a rectangularshape, a circular shape, an oval shape, an elliptical shape, pentagonalshape, a hexagonal shape, an octagonal shape or any polygonal shape. Invarious implementations, one or both of the major surface 31 a and 31 bcan have jagged edges such that the lateral dimensions (e.g., length orwidth) of the one or both of the major surface 31 a and 31 b variesacross the area of the one or both of the major surface 31 a and 31 b.Other configurations are also possible. Additionally, other shapes arealso possible. One or more of the edge surfaces can have a variety ofshapes (e.g., as viewed from the side), such as, for example, a squareshape, a rectangular shape, an oval shape, an elliptical shape, apentagonal shape, a hexagonal shape, an octagonal shape or any apolygonal shape.

The shape of the one or more of the edge surfaces (e.g., as viewed fromthe side) can be rectilinear or curvilinear in certain implementations.The shape may be regular or irregular in certain implementations.Similarly, the cross-section through the dielectric region 30 a and/or30 b parallel to one of the major surfaces 31 a and 31 b, can berectilinear or curvilinear in certain implementations and can be regularor irregular in certain implementations. For example, the cross-sectioncan have a square shape, a rectangular shape, a circular shape, an ovalshape, an elliptical shape, pentagonal shape, a hexagonal shape, anoctagonal shape or any a polygonal shape. Other shapes are alsopossible. Likewise, the cross-section through the dielectric material orregion 30 a and/or 30 b perpendicular to one of the surfaces 31 a and 31b, can be rectilinear or curvilinear in certain implementations and canbe regular or irregular implementations. For example, the cross-sectioncan have a square shape, a rectangular shape, a circular shape, an ovalshape, an elliptical shape, pentagonal shape, a hexagonal shape, anoctagonal shape or any a polygonal shape. Other shapes are alsopossible. In various implementations, an area, a length and/or a widthof the major surfaces 31 a and 31 b of the dielectric region 30 a can begreater than or equal to about 2, 3, 4, 5, 6, 8, or 10 times thethickness of the dielectric region 30 a and less than or equal to about50 times the thickness of the dielectric region 30 a, or any value in arange/sub-range between any of these values. Accordingly, the dielectricregion 30 a can have a large aspect ratio.

In some implementations, a thickness (T) of the dielectric region 30 acan correspond to the distance between the two major surfaces 31 a and31 b along a vertical direction as shown in FIG. 19A. As anotherexample, as shown in FIG. 19B, the dielectric material 30 b can beconfigured as a sphere. A thickness of the dielectric material 30 bconfigured as a sphere can correspond to the diameter of the sphere. Inother implementations, the dielectric material 30 a and/or 30 b can beconfigured as a cube, a rectangular cuboid, a cylinder, an ellipsoid, anovoid or any other three-dimensional shape. The shape may be curvilinearor rectilinear in certain implementations. The shape may be regular orirregular in certain implementations. Accordingly, in someimplementations, the dielectric region 30 a and/or 30 b can beconfigured as an irregularly shaped object enclosing a volume of one ormore dielectric materials.

In various implementations, light can be transmitted through the opticalstructure 70 a or 70 b and reflected by surfaces of the opticalstructure 70 a or 70 b. Moreover, in various implementations, thedielectric region 30 a and/or 30 b can have a thickness that allowslight incident on one side of the metal layer 35 a and/or 35 b toconstructively or destructively interfere. For example, in variousimplementations, the thickness of the dielectric region 30 a and/or 30 bcan be approximately a quarter wavelength of light (e.g., visible light)incident thereon or an integer multiple of a quarter wavelength. Invarious implementations, the thickness of the dielectric region 30 aand/or 30 b may be, for example, ¼, ¾, 5/4, 7/4, 9/4, 10/4, etc. of thewavelength of visible light incident on the dielectric material 30 a or30 b. As a result various wavelengths of incident light canconstructively or destructively interfere as it is transmitted throughthe optical structure 70 a or 70 b or reflected by the optical structure70 a or 70 b. Accordingly, in some configurations, color light isreflected by and/or transmitted through the optical structure when whitelight is incident thereon. In some implementations, a first color isreflected and a second different color is transmitted when white lightis incident on the optical structure. In some case, the first color andthe second color can be complementary.

In various implementations, for example, to obtain constructiveinterference of incident visible light, a thickness (or lateraldimension) of the dielectric region 30 a and/or 30 b can have a valuebetween about 90 nm and about 2 microns. In various implementations, athickness (or lateral dimension) of the dielectric region 30 a and/or 30b can be greater than or equal to about 90 nm and less than or equal toabout 1 microns, greater than or equal to about 100 nm and less than orequal to about 1.0 microns, greater than or equal to about 300 nm andless than or equal to about 1.0 microns, greater than or equal to about400 nm and less than or equal to about 900 nm, greater than or equal toabout 500 nm and less than or equal to about 800 nm, greater than orequal to about 600 nm and less than or equal to about 700 nm, or anythickness in any range/sub-range defined by these values. Values outsidethese ranges are also possible, in some implementations.

The dielectric material 30 a and/or 30 b can be purchased from varioussuppliers (e.g., Tyndall Institute, Glassflake, Ltd., SigmaTechnologies) or custom made by synthesizing in a laboratory or amanufacturing facility. In some implementations, the optical structure70 a (or 70 b) and/or the dielectric region 30 a (or 30 b) can compriseflakes (e.g., glass flakes available from Glassflake, Ltd.http://www.glassflake.com/pages/home). In some implementations, theflakes can comprise glass such as, for example, borosilicate flakeshaving an average thickness between about 90 nm and about 2 microns(e.g., an average thickness of about 1.2 microns) that may or may not becoated with coatings (e.g., high refractive index metal oxides such asTiO₂ and/or silica). In various implementations, lateral dimensions(e.g., length and a width) of the flakes can be between about 5 micronsand about 20 microns. Values outside these ranges are also possible, insome implementations.

As discussed above, the dielectric region 30 a or 30 b can be surroundedby a partially reflective and a partially transmissive metal layer 35 aor 35 b. In some implementations, the metal layer 35 a or 35 b cancomprise a metal having a ratio of the real part (n) of the refractiveindex to the imaginary part (k) of the refractive index (k) that is lessthan 1 as discussed above. For example, the metal layer 35 a or 35 b cancomprise metals that have an n/k value between about 0.01 and about 0.6,between about 0.015 and about 0.6, between about 0.01 and about 0.5,between about 0.01 and about 0.2, between about 0.01 and about 0.1, orany value in a range or sub-range defined by these values. Valuesoutside these ranges are also possible, in some implementations.Accordingly, the metal layer 35 a or 35 b can comprise silver, silveralloys, gold, aluminum or copper and their respective alloys, nickel(Ni) and palladium (Pd).

In various implementations, a thickness of the metal layer 35 a or 35 bcan be configured such that the metal layer 35 a or 35 b is at leastpartially transmissive and partially reflective to light in the visiblespectral region between about 400 nm and about 800 nm. For example, thethickness of the metal layer 35 can be configured such that the metallayer 35 a or 35 b is at least partially transmissive to light in awavelength range between about 400 nm and about 500 nm, between about430 nm and about 520 nm, between about 450 nm and about 530 nm, betweenabout 520 nm and about 550 nm, between about 540 nm and about 580 nm,between about 550 nm and about 600 nm, between about 600 nm and about680 nm, between about 630 nm and about 750 nm, or any wavelength in arange/sub-range defined by any of these values. Values outside theseranges are also possible, in some implementations. Alternatively or inaddition, the thickness of the metal layer 35 a or 35 b can beconfigured such that the metal layer 35 a or 35 b is at least partiallyreflective to light in a wavelength range between about 400 nm and about500 nm, between about 430 nm and about 520 nm, between about 450 nm andabout 530 nm, between about 520 nm and about 550 nm, between about 540nm and about 580 nm, between about 550 nm and about 600 nm, betweenabout 600 nm and about 680 nm, between about 630 nm and about 750 nm, orany wavelength in a range/sub-range defined by any of these values.Values outside these ranges are also possible, in some implementations.

The thickness of the metal layer 35 a or 35 b can vary depending on thetype of metal. For example, in implementations of the optical structure70 a or 70 b comprising a metal (e.g., silver) layer 35 a or 35 b, thethickness of the metal (e.g., silver) layer 35 a or 35 b can be greaterthan or equal to about 10 nm and less than or equal to about 35 nm suchthat the metal (e.g., silver) layer 35 a or 35 b can be partiallytransmissive to light in the visible spectral range. In someimplementations, the thickness of the metal layer 35 a or 35 b can beless than about 10 nm or greater than about 35 nm depending possibly onthe type of metal used and the wavelength range in which transmissivityor transmittance is desired. Accordingly, in various implementations,the metal layer 35 a or 35 b can have a thickness greater than or equalto about 3 nm and less than or equal to about 40 nm. Values outsidethese ranges are also possible, in some implementations. As discussedabove, with reference to FIG. 14, the thickness of the metal layer 35 aor 35 b and the dielectric region 30 a or 30 b can be configured suchthat interference of some or all of the incident light reflected by themetal layer 35 a or 35 b and the one or more layers of the dielectricregion 30 a or 30 b can produce a node at or in the metal layer 35 a or35 b. Accordingly, the transmittance through the metal layer 35 a or 35b can be greater than the transmittance expected for a certain thicknessof the metal layer 35 a or 35 b. Without subscribing to any particularscientific theory, this effect is known as induced transmittance. As aresult of induced transmittance or induced transmission, the opticalstructure 70 a or 70 b may in some implementation, be configured toexhibit a first color in reflection mode and a second color intransmission mode.

Depending on the shape of the dielectric region 30 a or 30 b, thedielectric region 30 a or 30 b can have one or more outer surfaces. Themetal layer 35 a or 35 b can cover or substantially cover all the outersurfaces of the dielectric region 30 a or 30 b or a fraction thereof.Accordingly, in various implementations, the metal layer 35 a or 35 bcan be disposed over at least 50% of the one or more outer surfaces ofthe dielectric region 30 a or 30 b. For example, metal layer 35 a or 35b can be disposed over at least 50%, over at least 60%, at least 75%, atleast 80%, at least 85%, at least 90%, at least 95%, at least 99%, 100%,or any range between any of these values of the one or more outersurfaces of the dielectric region 30 a or 30 b. In some implementations,the metal layer 35 a or 35 b can be disposed over the entire area (e.g.,100%) of the one or more outer surfaces of the dielectric region 30 a or30 b. Without subscribing to any particular theory, the opticalproperties of the optical structure 70 a or 70 b can vary based on theamount of outer surface of the dielectric region 30 a or 30 b that iscovered by the metal layer 35 a or 35 b. For example, the reflectivityor reflectance and/or the transmissivity or transmittance of the opticalstructure 70 a or 70 b can vary based on the amount of outer surface ofthe dielectric region 30 a or 30 b that is covered by the metal layer 35a or 35 b.

In various implementations, the shape of the metal layer 35 a or 35 bcan conform to the shape of the underlying dielectric material 30 a or30 b. For example, in the optical structure 70 a shown in FIG. 19A, thedielectric material 30 a has a rectangular cross-section. Accordingly,the metal layer 35 a which is disposed over the major surfaces 31 a and31 b and the edge surfaces also has a rectangular cross-section. Asanother example, in the optical structure 70 b shown in FIG. 19B, thedielectric material 30 b has a circular cross-section. Accordingly, themetal layer 35 b which is disposed over the circumference of thedielectric material 30 b also has a circular cross-section. However, inother implementations, the shape of the metal layer 35 a or 35 b can bedifferent from the shape of the underlying dielectric material 30 a or30 b.

In various implementations, the optical structure 70 a or 70 bcomprising a dielectric region 30 a or 30 b surrounded by a metal layer35 a or 35 b can be configured as particles, slabs, filaments, flakes,beads (e.g., spherical beads) or platelets as discussed above. In someimplementations, the optical structure 70 a or 70 b comprising adielectric region 30 a or 30 b surrounded by a metal layer 35 a or 35 bcan have the same shape as the shape of the dielectric region 30 a or 30b. For example, the optical structure 70 a can be configured as a cubeor a rectangular cuboid when the dielectric region 30 a is configured asa cube or a rectangular cuboid as shown in FIG. 19A. As another example,the optical structure 70 b can be configured as a sphere when thedielectric region 30 b is configured as a sphere as shown in FIG. 19B.In some cases, the optical structure 70 a or 70 b configured as aparticle, a slab, a flake, a filament, or a platelet can be suitable fora pigment or a printing ink. In some implementations, the opticalstructure 70 a or 70 b configured as a particle, a slab, a flake, afilament, or a platelet can have an area (or a lateral dimension) thatis about 5 to 10 times or more the thickness of the optical structure 70a or 70 b configured as a particle, a slab, a flake, a filament, or aplatelet. Accordingly, an optical structure 70 a or 70 b configured as aparticle, a slab, a flake, a filament, or a platelet can have athickness between about 100 nm and about 1 micron. In some suchimplementations, the area (or a lateral dimension) can be greater thanor equal to about 500 nm and less than or equal to about 1 micron,greater than or equal to about 1 micron and less than or equal to about5 microns, greater than or equal to about 5 microns and less than orequal to about 10 microns, greater than or equal to about 5 micron andless than or equal to about 40 microns, greater than or equal to about 5microns and less than or equal to about 20 microns, or any value in theranges/sub-ranges defined by these values. In various embodiments, theoptical structure 70 a or 70 b configured as a particle, a slab, aflake, a filament, or a platelet can be configured such that an area, alength and/or a width of a major surface of the optical structure 70 aor 70 b is greater than or equal to about 2, 3, 4, 5, 6, 8, or 10 timesthe thickness of the optical structure 70 a or 70 b and less than orequal to about 50 times the thickness of the optical structure 70 a or70 b or any value in any range formed by any of these values.

In various implementations, surrounding the dielectric region 30 a or 30b with the metal layer 35 a or 35 b can advantageously increase thereflectivity or reflectance of the dielectric material 30 a or 30 b atone or more wavelengths of the visible spectral range in someimplementations. In some implementations, surrounding the dielectricmaterial 30 a or 30 b with the metal layer 35 a or 35 b canadvantageously enhance or change the color appearance of the dielectricmaterial 30 a or 30 b at one or more wavelengths of the visible spectralrange in reflection and transmission mode.

In various implementations, the optical structure 70 a or 70 bcomprising the dielectric region 30 a or 30 b surrounded by the metallayer 35 a or 35 b can have a reflection spectrum with one or morereflection peaks in the visible spectral region and a transmissionspectrum with one or more transmission peaks in the visible spectralregion. Without any loss of generality, the one or more reflection peaksand the one or more transmission peak do not overlap with each other.Accordingly, the optical structure 70 a or 70 b comprising thedielectric region 30 a or 30 b surrounded by the metal layer 35 a or 35b can have a first color in the reflection mode and a second colordifferent from the first color in the transmission mode. In certainimplementations, the first color and the second color can becomplementary colors, such as, for example, red and green, yellow andviolet, blue and orange, green and magenta, etc.

In various implementations, there may be little to no shift in the firstcolor in the reflection mode for any viewing angle between a first anglewith respect to a normal to the surface of the optical structure 70 a or70 b and a second angle with respect to a normal to the surface of theoptical structure 70 a or 70 b. Likewise, in some implementations, theremay be little to no shift in the second color in the transmission modefor any viewing angle between a first angle with respect to a normal tothe surface of the optical structure 70 a or 70 b and a second anglewith respect to a normal to the surface of the optical structure 70 a or70 b. In various implementations, the first angle can have a valuebetween 0 degrees and 10 degrees (e.g., 0 degrees, 1 degree, 2 degrees,3 degrees, 4 degrees, 5 degrees, 6 degrees, 7 degrees, 8 degrees, 9degrees or 10 degrees). In various implementations, the second angle canhave a value between 20 degrees and 90 degrees (e.g., 20 degrees, 30degrees, 40 degrees, 50 degrees, 60 degrees, 70 degrees, 80 degrees or90 degrees). Accordingly, for any viewing angle between a first angle(e.g., 0 degrees, 1 degree, 2 degrees, 3 degrees, 4 degrees, 5 degrees,6 degrees, 7 degrees, 8 degrees, 9 degrees or 10 degrees) with respectto a normal to the surface of the optical structure 70 a or 70 b and asecond angle (e.g., 20 degrees, 30 degrees, 40 degrees, 50 degrees, 60degrees, 70 degrees, 80 degrees or 90 degrees) with respect to a normalto the surface of the optical structure 70 a or 70 b, the color of theoptical structure 70 a or 70 b in the reflection mode and/or thetransmission mode may remain substantially the same. Likewise, in someimplementations, there may be little to no shift color shift in thecolor of the optical structure 70 a or 70 b in the reflection modeand/or the transmission mode for tilt of 10 degrees, 20 degrees, 30degrees, 40 degrees, 50 degrees, 60 degrees, 70 degrees, 80 degrees or90 degrees or any value in a range/sub-range defined by any of thesevalues.

In some implementations, it may be desirable to have a color shift inthe first color in the reflection mode as the viewing angle changes froma first angle with respect to a normal to the surface of the opticalstructure 70 a or 70 b to a second angle with respect to a normal to thesurface of the optical structure 70 a or 70 b. Similarly, in variousimplementations, it may be desirable to have a color shift in the secondcolor in the transmission mode as the viewing angle changes from a firstangle with respect to a normal to the surface of the optical structure70 a or 70 b to a second angle with respect to a normal to the surfaceof the optical structure 70 a or 70 b. In various implementations, thefirst angle can have a value between 0 degrees and 10 degrees (e.g., 0degrees, 1 degree, 2 degrees, 3 degrees, 4 degrees, 5 degrees, 6degrees, 7 degrees, 8 degrees, 9 degrees or 10 degrees). In variousimplementations, the second angle can have a value between 20 degreesand 90 degrees (e.g., 20 degrees, 30 degrees, 40 degrees, 50 degrees, 60degrees, 70 degrees, 80 degrees or 90 degrees) depending on the design.Accordingly, as the viewing angle changes from a first angle (e.g., 0degrees, 1 degree, 2 degrees, 3 degrees, 4 degrees, 5 degrees, 6degrees, 7 degrees, 8 degrees, 9 degrees or 10 degrees) with respect toa normal to the surface of the optical structure 70 a or 70 b to asecond angle with respect to a normal to the surface of the opticalstructure 70 a or 70 b and a second angle (e.g., 20 degrees, 30 degrees,40 degrees, 50 degrees, 60 degrees, 70 degrees, 80 degrees or 90degrees) with respect to a normal to the surface of the opticalstructure 70 a or 70 b, the color of the optical structure 70 a or 70 bin the reflection mode and/or the transmission mode may change (e.g.,dark blue to light blue, purple to pink, dark green to light green,etc.). Likewise, in some implementations, there may be a shift in thecolor of the optical structure 70 a or 70 b in the reflection modeand/or the transmission mode for tilt of 10 degrees, 20 degrees, 30degrees, 40 degrees, 50 degrees, 60 degrees, 70 degrees, 80 degrees or90 degrees or any value in a range/sub-range defined by any of thesevalues.

Without subscribing to any particular theory, the one or more reflectionpeaks of the reflection spectrum of the optical structure 70 a or 70 bcomprising the dielectric region 30 a or 30 b surrounded by the metallayer 35 a or 35 b can have high reflectivity or reflectance. Forexample, the reflectivity or reflectance of the one or more reflectionpeaks can be greater than or equal to 30%, greater than or equal to 40%,greater than or equal to 50%, greater than or equal to 55%, greater thanor equal to 60%, greater than or equal to 65%, greater than or equal to70%, greater than or equal to 75%, greater than or equal to 80%, greaterthan or equal to 85%, greater than or equal to 90%, greater than orequal to 95% and less than or equal to 100%, or a value in anyrange/sub-range defined by these values.

Without subscribing to any particular theory, the one or moretransmission peaks of the transmission spectrum of the optical structure70 a or 70 b comprising the dielectric region 30 a or 30 b surrounded bythe metal layer 35 a or 35 b can have high transmissivity ortransmittance. For example, the transmissivity or transmittance of theone or more transmission peaks can be greater than or equal to 30%,greater than or equal to 40%, greater than or equal to 50%, greater thanor equal to 55%, greater than or equal to 60%, greater than or equal to65%, greater than or equal to 70%, greater than or equal to 75%, greaterthan or equal to 80%, greater than or equal to 85%, greater than orequal to 90%, greater than or equal to 95% and less than or equal to100%, or a value in any range/sub-range defined by these values.

The optical structures 70 a and 70 b comprising the dielectric region 30a or 30 b surrounded by the metal layer 35 a or 35 b can produce many orall the optical effects that are described above with reference tooptical structure 10 where the two metal layers 13 and 15 do notsurround the dielectric layer 14 (e.g., as shown in FIG. 11).

The metal layer 35 a or 35 b can be disposed around the dielectricmaterial 30 a or 30 b using a variety of chemical methods. For example,metal layer 35 a or 35 b can be disposed around the dielectric region 30a or 30 b using electroless method. Various implementations of anelectroless method of depositing the metal layer 35 a or 35 b cancomprise depositing the metal layer 35 a or 35 b without applyingelectrical current or voltage. Various metals such as, for example,gold, silver, or nickel can be deposited using electroless methods. Anexample of depositing metal layer 35 a or 35 b comprising silver aroundthe dielectric region 30 a or 30 b using an electroless method isdiscussed below. The electroless method of depositing silver can also bereferred to as electroless silver plating. Electroless silver platingcomprises immersing the dielectric region 30 a or 30 b in a silveringbath comprising chemical compounds of silver (e.g., silver nitrate,silver-ammonia compounds, sodium argento cyanide, etc.) and at least oneof ammonia, water, potassium hydroxide or sodium hydroxide. The chemicalcompounds of silver are reduced to metallic silver using a reducingagent which is added to the silvering bath. The metallic silver adheresto the exposed surfaces of the dielectric region 30 a or 30 b. Thereducing agent can comprise glucose, sucrose, invert sugar, stannouschloride, hydrazine, Rochelle salt, formaldehyde, or organic borane(e.g., dimethylamine borane in various implementations). In certainimplementations, the silvering bath and the reducing agent can besprayed on the dielectric region 30 a or 30 b. In some implementations,the outer surface of the dielectric region 30 a or 30 b can be activatedusing stannous chloride (SnCl₂) in preparation for the electrolessdeposition of the metal layer. Other methods of depositing the metallayer 35 a or 35 b on the outer surface of the dielectric region 30 a or30 b can also be used. For example, the metal layer 35 a or 35 b can bedisposed around the dielectric region 30 a or 30 b using methods suchas, for example, chemical vapor deposition (CVD), sputtering orelectroplating. In some implementations, the metal layer 35 a or 35 bcan be patterned around the dielectric region 30 a or 30 b.

In various implementation, a second dielectric region 40 a or 40 bcomprising one or more dielectric materials may be disposed around themetal coated dielectric region 30 a or 30 b. The second dielectricregion 40 a or 40 b may comprise high refractive index materials such asZrO₂, TiO₂, ZnS, ITO (indium tin oxide), CeO₂ or Ta₂O₃. In variousimplementations, the second dielectric region 40 a or 40 b may comprisedielectric materials having refractive index greater than 1.65 and lessthan or equal to 2.5. For example, the refractive index of the one ormore dielectric material in the second dielectric region 40 a or 40 bcan be greater than or equal to 1.65 and less than or equal to 1.75,greater than or equal to 1.75 and less than or equal to 1.85, greaterthan or equal to 1.85 and less than or equal to 1.95, greater than orequal to 1.95 and less than or equal to 2.05, greater than or equal to2.0 and less than or equal to 2.2, greater than or equal to 2.1 and lessthan or equal to 2.3, greater than or equal to 2.25 and less than orequal to 2.5, or any value in any range/sub-range defined by thesevalues. Other values outside these ranges are also possible in someimplementations. In various implementations, the refractive index of theone or more materials of the second dielectric region 40 a or 40 b canbe greater than the refractive index of the one or more materials of thedielectric region 30 a or 30 b. The thickness of the second dielectricregion 40 a or 40 b can be between 75 nm and 700 nm. For example, thethickness of the second dielectric region 40 a or 40 b can be greaterthan or equal to 75 nm and less than or equal to 100 nm, greater than orequal to 100 nm and less than or equal to 150 nm, greater than or equalto 150 nm and less than or equal to 200 nm, greater than or equal to 200nm and less than or equal to 250 nm, greater than or equal to 300 nm andless than or equal to 350 nm, greater than or equal to 400 nm and lessthan or equal to 450 nm, greater than or equal to 450 nm and less thanor equal to 500 nm, greater than or equal to about 500 nm and less thanor equal to 650 nm, greater than or equal to 650 nm and less than orequal to 700 nm, or any value in any range/sub-range defined by thesevalues. The second dielectric region 40 a or 40 b can be disposed tocover at least 50% of the outer surface of the metal layer 35 a or 35 b.For example, the second dielectric region 40 a or 40 b can be disposedto cover at least 80%, at least 90%, at least 95%, or 100% of the outersurface of the metal layer 35 a or 35 b, or any value in arange/sub-range defined by these values.

The reflected color and/or the transmitted color of the opticalstructure 70 a or 70 b comprising the second dielectric region 40 a or40 b surrounding the metal coated dielectric region 30 a or 30 b can bedifferent from the reflected color and/or the transmitted color of theoptical structure 70 a or 70 b comprising only the metal coateddielectric region 30 a or 30 b. For example, the reflected color and/orthe transmitted color of the optical structure 70 a or 70 b comprisingthe second dielectric region 40 a or 40 b surrounding the metal coateddielectric region 30 a or 30 b can be more vibrant than the reflectedcolor and/or the transmitted color of the optical structure 70 a or 70 bcomprising the metal coated dielectric region 30 a or 30 b without thesecond dielectric region 40 a or 40 b having suitable thickness and/ormaterials with suitable refractive index. The shape of the transmissionand/or reflection peaks, the position of the maximum of the transmissionand/or reflection peaks and/or the width (e.g., full width at halfmaximum (FWHM)) of the transmission and/or reflection peaks of theoptical structure 70 a or 70 b comprising the second dielectric region40 a or 40 b surrounding the metal coated dielectric region 30 a or 30 bcan be different from the shape of the transmission and/or reflectionpeaks, the position of the maximum of the transmission and/or reflectionpeaks and/or the width of the transmission and reflection peaks of theoptical structure 70 a or 70 b comprising the metal coated dielectricregion 30 a or 30 b without the second dielectric region 40 a or 40 bhaving suitable thickness and/or materials with suitable refractiveindex. For example, the width of one or more of the reflection peaks ofthe optical structure 70 a or 70 b comprising the second dielectricregion 40 a or 40 b surrounding the metal coated dielectric region 30 aor 30 b can be broader than the width of a corresponding reflection peakof the optical structure 70 a or 70 b comprising the metal coateddielectric region 30 a or 30 b without the second dielectric region 40 aor 40 b having suitable thickness and/or materials with suitablerefractive index. As another example, the width (e.g., FWHM) of one ormore of the reflection peaks of the optical structure 70 a or 70 bcomprising the second dielectric region 40 a or 40 b surrounding themetal coated dielectric region 30 a or 30 b can be greater than or equalto about 50 nm and less than or equal to about 300 nm, in someimplementations.

Various implementations of the of the optical structure 70 a or 70 bcomprising the second dielectric region 40 a or 40 b surrounding themetal coated dielectric region 30 a or 30 b can have a reflectionspectrum with one or more reflection peaks having a width (e.g., FWHM)greater than or equal to about 10 nm, greater than or equal to about 20nm, greater than or equal to about 30 nm, greater than or equal to about40 nm, greater than or equal to about 50 nm, greater than or equal toabout 60 nm, greater than or equal to about 70 nm, greater than or equalto about 100 nm, greater than or equal to about 200 nm, less than orequal to about 300 nm, less than or equal to about 250 nm, or any valuein a range/sub-range defined by these values. Various implementations ofthe optical structure 70 a or 70 b comprising the second dielectricregion 40 a or 40 b surrounding the metal coated dielectric region 30 aor 30 b can have higher reflectivity or reflectance at one or morewavelengths in the visible spectral range as compared to thereflectivity or reflectance of the optical structure 70 a or 70 bcomprising the metal coated dielectric region 30 a or 30 b without thesecond dielectric region 40 a or 40 b having suitable thickness and/ormaterials with suitable refractive index at those one or morewavelengths in the visible spectral range.

Various implementations of the of the optical structure 70 a or 70 bcomprising the second dielectric region 40 a or 40 b surrounding themetal coated dielectric region 30 a or 30 b can have a transmissionspectrum with one or more transmission peaks having a width (e.g., FWHM)greater than or equal to about 10 nm, greater than or equal to about 20nm, greater than or equal to about 30 nm, greater than or equal to about40 nm, greater than or equal to about 50 nm, greater than or equal toabout 60 nm, greater than or equal to about 70 nm, greater than or equalto about 100 nm, greater than or equal to about 200 nm, less than orequal to about 300 nm, less than or equal to about 250 nm, or any valuein a range/sub-range defined by these values.

Without subscribing to any particular theory, the one or more reflectionpeaks of the reflection spectrum of the optical structure 70 a or 70 bcomprising the second dielectric region 40 a or 40 b surrounding themetal coated dielectric region 30 a or 30 b can have high reflectivityor reflectance. For example, the reflectivity or reflectance of the oneor more reflection peaks can be greater than or equal to 30%, greaterthan or equal to 40%, greater than or equal to 50%, greater than orequal to 55%, greater than or equal to 60%, greater than or equal to65%, greater than or equal to 70%, greater than or equal to 75%, greaterthan or equal to 80%, greater than or equal to 85%, greater than orequal to 90%, greater than or equal to 95% and less than or equal to100%, or a value in any range/sub-range defined by these values.

Without subscribing to any particular theory, the one or moretransmission peaks of the transmission spectrum of the optical structure70 a or 70 b comprising the second dielectric region 40 a or 40 bsurrounding the metal coated dielectric region 30 a or 30 b can havehigh transmissivity or transmittance. For example, the transmissivity ortransmittance of the one or more transmission peaks can be greater thanor equal to 30%, greater than or equal to 40%, greater than or equal to50%, greater than or equal to 55%, greater than or equal to 60%, greaterthan or equal to 65%, greater than or equal to 70%, greater than orequal to 75%, greater than or equal to 80%, greater than or equal to85%, greater than or equal to 90%, greater than or equal to 95% and lessthan or equal to 100%, or a value in any range/sub-range defined bythese values.

Additionally, the second dielectric region 40 a or 40 b canadvantageously insulate the metal layer 35 a or 35 b from the inkvarnish when the optical structures 70 a or 70 b are configured aspigments.

In some implementations, the second dielectric region 40 a or 40 b canbe disposed around the metal coated dielectric materials 30 a or 30 busing a sol-gel process. For example, the metal coated dielectricmaterials 30 a or 30 b can be coated with a dielectric materialcomprising titanium di-oxide (TiO₂) using a sol-gel process, involvingthe hydrolysis of titanium(IV) isopropoxide. As another example, aprecursor comprising the dielectric material 40 a or 40 b is transformedto form a colloidal suspension (or a “sol”) by a series of hydrolysisand polymerization reactions. In some implementations, the colloidalsuspension comprising the dielectric material of the second dielectricregion 40 a or 40 b can be disposed on the metal coated first dielectricregion 30 a or 30 b by a coating, gelling or precipitation. The metalcoated first dielectric region 30 a or 30 b comprising the colloidalsuspension comprising the dielectric material of the second dielectricregion 40 a or 40 b can be heated or dried to obtain the metal coatedfirst dielectric region 30 a or 30 b coated with second dielectricregion 40 a or 40 b. In some implementations, the one or more materialsof the second dielectric region 40 a or 40 b can be disposed around themetal coated first dielectric region 30 a or 30 b using depositionmethods such as, for example, chemical vapor deposition method, e-beam,sputtering. In some implementations, the various deposition methods canbe combined with vibrating the metal coated first dielectric region 30 aor 30 b.

As discussed above, various embodiments of the optical structures 10, 70a or 70 b are configured to partially reflect light and partiallytransmit light. In various implementations, the reflectivity orreflectance of the optical structures 10, 70 a or 70 b at one or morewavelengths in the visible spectral range can be greater than or equalto 10%, greater than or equal to 20%, greater than or equal to 30%,greater than or equal to 40%, greater than or equal to 50%, greater thanor equal to 60%, greater than or equal to 70%, greater than or equal to80%, greater than or equal to 90%, greater than or equal to 95% and/orless than or equal to 100%, or any value in any range/sub-range definedby these value. In various implementations, the transmissivity ortransmittance of the optical structures 10, 70 a or 70 b at one or morewavelengths in the visible spectral range can be greater than or equalto 10%, greater than or equal to 20%, greater than or equal to 30%,greater than or equal to 40%, greater than or equal to 50%, greater thanor equal to 60%, greater than or equal to 70%, greater than or equal to80%, greater than or equal to 90%, greater than or equal to 95% and/orless than or equal to 100%, or any value in any range/sub-range definedby these value. In various implementations, the reflectivity orreflectance of the optical structures 10, 70 a or 70 b at one or morefirst set of wavelengths can be approximately equal to thetransmissivity or transmittance of the optical structures 10, 70 a or 70b at one or more second set of wavelengths different from the first setof wavelengths.

The optical structures 10, 70 a or 70 b can have a size, such as, forexample, a lateral dimension, an area, a length or a width of theoptical structure (e.g., a length, a width or an area of a major surfaceof the optical structure) greater than or equal to about 1 micron andless than or equal to about 50 microns. For example, the size of theoptical structures 10, 70 a or 70 b can be greater than or equal toabout 1 micron and less than or equal to 10 microns, greater than orequal to 2 microns and less than or equal to 12 microns, greater than orequal to 3 microns and less than or equal to 15 microns, greater than orequal to 4 microns and less than or equal to 18 microns, greater than orequal to 5 microns and less than or equal to 20 microns, greater than orequal to 10 microns and less than or equal to 20 microns, greater thanor equal to 15 microns and less than or equal to 25 microns, greaterthan or equal to 20 microns and less than or equal to about 30 microns,greater than or equal to 25 microns and less than or equal to 35microns, greater than or equal to 30 microns and less than or equal to40 microns, greater than or equal to 35 microns and less than or equalto 45 microns, greater than or equal to 40 microns and less than orequal to 50 microns, or a value in any range/sub-range defined by thesevalues.

The optical structures 10, 70 a or 70 b can have a size, such as, forexample, a lateral dimension, an area, a length or a width of theoptical structure (e.g., a length, a width or an area of a major surfaceof the optical structure) greater than or equal to about 1 micron andless than or equal to about 50 microns can be between 0.1 microns and2.0 microns. For example, the thickness of the optical structures 10, 70a or 70 b having a size, such as, for example, a lateral dimension, anarea, a length or a width of the optical structure (e.g., a length, awidth or an area of a major surface of the optical structure) greaterthan or equal to 0.1 micron and less than or equal to 0.3 microns,greater than or equal to 0.2 microns and less than or equal to 0.5microns, greater than or equal to 0.3 microns and less than or equal to0.6 microns, greater than or equal to 0.4 microns and less than or equalto 0.7 microns, greater than or equal to 0.5 microns and less than orequal to 0.8 microns, greater than or equal to 0.6 microns and less thanor equal to 0.9 microns, greater than or equal to 0.7 microns and lessthan or equal to 1.0 micron, greater than or equal to 1.0 micron andless than or equal to 1.2 microns, greater than or equal to 1.2 micronsand less than or equal to 1.5 microns, greater than or equal to 1.5microns and less than or equal to 2.0 microns, or a value in anyrange/sub-range defined by these values.

One or more of the optical structures 10, 70 a or 70 b discussed abovecan be incorporated with or in a document (e.g., a banknote), package,product, or other item. Optical products such as a film, a thread, alaminate, a foil, a pigment, or an ink comprising one or more of theoptical structures 10, 70 a or 70 b discussed above can be incorporatedwith or in documents such as banknotes or other documents to verifyauthenticity of the documents, packaging materials, etc. For example,the optical structures 70 a or 70 b can be configured as an ink or apigment which is disposed on a base comprising at least one of apolymer, a plastic, a paper or a fabric. The base may be flexible insome implementations. The base comprising the ink or a pigment orpigment comprising the optical structures 70 a or 70 b can be cut ordiced to obtain a thread or a foil. A plurality of optical structures10, 70 a or 70 b discussed above can be incorporated in a particularoptical product (e.g., ink, pigment, thread, filament, paper, securityink, security pigment, security thread, security filament, securitypaper, etc.). The shapes, sizes and/or aspect ratios of the plurality ofoptical structures 10, 70 a or 70 b discussed above that areincorporated in a particular optical product (e.g., ink, pigment,thread, filament, paper, security ink, security pigment, securitythread, security filament, security paper, etc.) can vary. Accordingly,a particular optical product (e.g., ink, pigment, thread, filament,paper, security ink, security pigment, security thread, securityfilament, security paper, etc.) can comprise optical structures 10, 70 aor 70 b with different distributions of shapes, sizes and/or aspectratios of the optical structures. For example, a particular opticalproduct (e.g., ink, pigment, thread, filament, paper, security ink,security pigment, security thread, security filament, security paper,etc.) can comprise optical structures 10, 70 a or 70 b with sizesdistributed around one or more mean sizes. As another example, aparticular optical product (e.g., ink, pigment, thread, filament, paper,security ink, security pigment, security thread, security filament,security paper, etc.) can comprise optical structures 10, 70 a or 70 bwith aspect ratios distributed around one or more aspect ratios.

FIG. 20 shows, for example, a banknote 80 comprising a laminated film83. The laminated film 83 comprises the optical structure 10, 70 a or 70b. The laminated film 83 can be fabricated by disposing the opticalstructure 10, 70 a or 70 b over a base or support layer or substratesuch as polymer base layer (e.g., a polyester film). The opticalstructure 10, 70 a or 70 b can be disposed over the polymer base layerby a variety of methods including but not limited to coating methods,vacuum deposition on a surface of the polymer base layer, etc. Theoptical structure 10, 70 a or 70 b may be disposed over a first side ofthe surface of the polymer base layer (e.g., polyester film). Thelaminated film 83 can be adhered to the “paper” (e.g., cellulose,cotton/linen, polymer or fabric) 81 of the banknote 80, for example, bya transparent and/or an optically clear adhesive. In various cases, asecond surface of the polymer base layer opposite the first surface ofthe base layer is disposed closer to the banknote paper 81 comprisingthe banknote and may be in contact with the adhesive. In some cases, theadhesive can be a two component adhesive with one component disposedonto the banknote paper and the other component disposed on the secondsurface of the polymer base layer opposite the first surface of the baselayer on which the optical structure 10, 70 a or 70 b is disposed. Thebanknote 80 and the laminated film 83 can be brought together forbonding. The laminated film 83 can also be attached to the banknote 80using a cross-linking thermoset adhesive. A transparent protectivebarrier coating 82 (e.g., UV curable cross-linked resin) can be disposedover the laminated film 83. The protective barrier coating 82 can extendover the edges of the laminated film 83 onto the paper (e.g., fabric) 81of the banknote. The protective barrier coating 82 can be configured toprotect the laminated film 83 against corrosion, abrasive wear andliquids that may commonly come in contact with the banknote 80 withoutsacrificing the optical effects provided by the laminated film 83. Theoptical structure 10 can be disposed facing the protective barriercoating 82 or the adhesive layer between the laminated film 83 and the“paper” 81.

In some embodiments, the optical structure 10, 70 a or 70 b can beconfigured as a thread (e.g., a windowed thread) instead of a laminatedfilm. A windowed thread can be manufactured by a variety of methods. Forexample, the thread can be woven up and down within the paper and to thesurface of the paper during the papermaking process. As another example,the windowed thread can be disposed within the paper itself so that nopart of the thread reaches the surface of the banknote. As yet anotherexample, open spaces within the paper can be provided in the regions ofthe paper comprising the thread.

The thread can be fabricated by cutting a strip of the optical structure10, for example the web, sheet, or base layer on which the layerscomprising the optical structure 10 are formed and passing the stripthrough a bath of UV curable resin. The rate at which the strip ispassed through the UV curable resin bath can be controlled to coat thesides and the edges of the strip uniformly. The strip coated with the UVcurable resin can be cured to obtain the thread. The obtained threadcomprising the optical structure 10 can be inserted (e.g., weaved) inthe banknote. In some implementations, any fringe (e.g., the jagged orragged edge of the thread) of the thread (due to hot stamping or chatterfrom any cutting operation) can be hidden from an observer by printingan opaque border around the hot stamp patch. Another way to affix theoptical structure 10, 70 a or 70 b to the banknote can include diecutting a portion of the optical structure, for example, the web, sheet,or base layer on which the layers comprising the optical structure 10,70 a or 70 b are formed and applying the portion to the banknote usingan adhesive. Various implementations of the examples of opticalstructure described above can be configured as a thread, a hot stamp, ora laminate and incorporated with or in a document (e.g., a banknote),package, product, or other item.

Without any loss of generality, the optical structure 10, 70 a or 70 bor a material (e.g., an ink, a paint or a pigment, a varnish) comprisingthe optical structure 10, 70 a or 70 b can be disposed on a basecomprising at least one of a polymer, a plastic, a paper or a fabric.The base comprising the optical structure 10, 70 a or 70 b or thematerial comprising the optical structure 10, 70 a or 70 b can be cut ordiced into a smaller portions having a variety of shapes and/or sizes.The smaller portions can be disposed on or inserted into or onto asubstrate (e.g., a bank note, paper, packaging material, fabric, etc.)using various methods. For example, the smaller portions can beconfigured as strips or threads which can be woven into the substrate.As another example, the smaller portions can be configured as foilswhich can be hot stamped on the substrate. As yet another example, thesmaller portions can be laminated to the substrate using adhesives.

FIG. 21A depicts a banknote 90 a having two transparent windows 91 a and92 a inserted into or attached on the paper (e.g., fabric) of thebanknote. Each window comprises the optical structure 10, 70 a or 70 b.In some implementations, the reflection and/or transmission spectra ofthe optical structure 10 of the window 91 a may be configured to bedifferent from the reflection and/or transmission spectra of the opticalstructure 10, 70 a or 70 b of the window 92 a. Thus, a person viewingthe banknote 90 a will perceive a first reflected color when viewing thewindow 91 a along a viewing direction (e.g., normal to the surface ofthe banknote 90 a) and a second reflected color different from the firstreflected color when viewing the window 92 a along the viewingdirection. The person may also perceive a third transmitted colordifferent from the first reflected color when viewing through the window91 a along the viewing direction. The person may additionally perceive afourth transmitted color different from the first, second and thirdcolors when viewing through the window 92 a along the viewing direction.Furthermore, upon folding the banknote 90 a over itself so that the twowindows 91 a and 92 a are at least partially aligned with respect to oneanother, the person will perceive a different color, different from thefirst, second, third and/or fourth colors in reflection and transmissionmodes when viewing the banknote 90 a along the viewing direction. Forexample, upon folding the banknote 90 a over itself so that the twowindows 91 a and 92 a are at least partially aligned with respect to oneanother, the person will perceive a reflected color that is acombination of the effects of the reflectivity or reflectance spectrumsof the two windows 91 a and 92 a and a transmitted color that is acombination of the effects of the transmission spectrums of the twowindows 91 a and 92 a. Additionally, the person can perceive color shiftof the various colors seen in the reflection and transmission modes asthe viewing angle changes. The amount of color shift may be differentfrom the different windows as well as for the combination of the twowindows.

FIG. 21B depicts an implementation of a security device 90 b (e.g., abanknote) comprising two windows 91 b and 92 b (a first and a second)inserted into or attached to the surface of the security device 90 b.The two windows 91 b and 92 b at least partially overlap in theoverlapping region 93 b. The two windows 91 b and 92 b are transparentand comprise the optical structure 10, 70 a or 70 b. The configuration(e.g., thickness or other design parameters) of the optical structures10, 70 a or 70 b in the respective windows 91 a and 91 b can be suchthat the reflection and/or transmission spectra of the optical structure10, 70 a or 70 b of the window 91 b is different from the reflectionand/or transmission spectra of the optical structure 10 of the window 92b.

Thus, a person viewing the security device 90 b along a viewingdirection (e.g., normal to the surface of the security device 90 b) willperceive (i) a first reflected color when viewing the portion of thewindow 91 b that does not overlap with the window 92 b, (ii) a secondreflected color different from the first color when viewing the portionof the window 92 b that does not overlap with the window 91 b; and (iii)a third second reflected color that is a combination of the effects ofthe reflectivity or reflectance spectrums of the two windows 91 b and 92b when viewing the overlapping region 93 b.

A person viewing the security device 90 b along a viewing direction(e.g., normal to the surface of the security device 90 b) will perceive(i) a fourth transmitted color different from the first color whenviewing through the portion of the window 91 b that does not overlapwith the window 92 b, (ii) a fifth transmitted color different from thesecond and the fourth color when viewing through the portion of thewindow 92 b that does not overlap with the window 91 b; and (iii) asixth transmitted color that is a combination of the effects of thetransmission spectrums of the two windows 91 b and 92 b when viewingthrough the overlapping region 93 b.

Additionally, in various embodiments, a person viewing the securitydevice 90 b can perceive color shift of the various colors seen in thereflection and transmission modes as the viewing angle changes. Theamount of color shift may be different from the different windows.

Although, the two windows 91 b and 92 b are shown as partiallyoverlapping in FIG. 21B, the two windows 91 b and 92 b can be completelyoverlapping. Various implementations of the security device 90 b cancomprise two or more different pigments. The two or more differentpigments can comprise optical structures 10. A respective opticalstructure of one of the two or more different pigments can havereflectance and transmittance characteristics that are different fromthe respective optical structure of another of the two or more differentpigments. The two or more different pigments can partially or completelyoverlap with each other. As discussed above, the color perceived by aperson viewing an overlapping region of the two or more differentpigments can depend on a combination of the effects of thereflection/transmission spectra of the different optical structures ofthe two or more different pigments. Some implementations of the securitydevice 90 b can comprise two or more at least partially overlappingfoils, films, threads or laminates comprising different opticalstructures. The color perceived by a person viewing an overlappingregion of the two or more at least partially overlapping foils, films,threads or laminates can depend on a combination of the effects of thereflection/transmission spectra of the different optical structures ofthe two or more foils, films, threads or laminates.

FIG. 22 illustrates a side view of an object 100 with a security devicecomprising a main body 103 of the object and a layer 102 comprising theoptical structure 10, 70 a or 70 b. The object can be a banknote. Themain body may comprise paper comprising the banknote. The layer 102 canbe a laminate, a thread, or a label. When the layer 102 is configured asa label, an adhesive (e.g., a varnish) can be applied to the main body103 and the layer 102 can be adhered to the adhesive of the main body103 using a polymeric adhesive. Alternatively, the adhesive can beapplied to the layer 102 before being affixed to the main body 103. Whenthe layer 102 is configured as a laminate, the layer 102 can be adheredto the main body 103 using a polymer.

The layer 102 can be adhered to the main body 103 using adhesives, suchas, for example optical clear adhesive and/or a cross-linking thermosetadhesive. The security device 100 further comprises a layer 101comprising a message that is composed using a text, a symbol, a numberor any combination thereof that is disposed on the side of the main body(e.g., paper/fabric) 103 of the object (e.g., banknote) opposite theside on which the layer 102 as shown in FIG. 22. Alternately, the layer101 can be disposed between the main body (e.g., paper/fabric) 103 andthe layer 102 or over the layer 102. The layer 101 can comprise, forexample, a dye, a pigment or a phosphorescent material that has the samecolor characteristics as the color reflected or transmitted by theoptical structure 10 when viewed along a direction normal to the surfaceof the layer 102. Accordingly, the message is not visible to an observer(or hidden) when the security device 100 is viewed along a directionnormal to the surface of the layer 102. However, when the securitydevice 100 is tilted such that viewing angle changes, the colorreflected by and/or transmitted through the optical structure 10 changessuch that the message become visible to the observer. In certain cases,the layer 101 comprising a message printed with a phosphorescentmaterial can be made visible when illuminated by UV. The resultant colorof the phosphorescent material can be the combined color of thefluoresence and the dichroic color.

FIG. 23 shows the effect of changing the viewing angle in transmissionof the security device 100 from 0 to about 45 degrees. When the viewingangle is 0 degrees, the message comprising a combination of a number,text or a symbol is not visible in the transmission mode because thecolor of the text is the same as the color of the optical structure intransmission mode (e.g., orange). However, as the viewing angleincreases, the color of the optical structure in transmission modeshifts. For example, the message 203 becomes visible as the color of theoptical structure in transmission mode shifts from orange to yellow asthe angle of observation increases. The color of the message hassufficient contrast with respect to the transmitted color of the opticalstructure 10 so as to be visible to the observer.

In other embodiments, the security device 100 can be configured tooperate in reverse to that described above such that for example themessage is visible at normal incidence and not visible when the securitydevice is tilted. Other variations are possible.

As describe above, the optical structures 10, 70 a or 70 b may be usedin different forms, such as a laminate, a foil, a film, a hot stamp, athread, pigment, ink, or paint. In some implementations, a laminate, afoil, a film, or a thread can comprise a pigment, ink or paintcomprising the optical structures 10, 70 a or 70 b. A laminate may beadhered to a document, product or package using adhesive. A thread maybe threaded or woven through an opening, for example, in the document. Afoil can be hot stamped on the document, product or package. Pigment,ink, or paint may be deposited on the document, product or package orthe material (e.g., paper, cardboard, or fabric) used to form thedocument, product, or package. For example, the document, product, orpackage may be exposed to (e.g., contacted with) the pigment, ink, orpaint to color the document, product or packages in process similar tothose used for non-color shifting pigments, dyes, paints and inks.

A plurality of optical structures 10, 70 a or 70 b such as describedherein collected together as a pigment (as well as inks, and paints) canhave similar optical characteristics as the optical structure 10, 70 aor 70 b configured as a film/laminate. As described above, opticalstructures 10, 70 a or 70 b collected together to form a pigments canexhibit as a collection of platelets or separate pieces the same opticalcharacteristics as the bulk optical film from which the platelets weremade. An added advantage of the optical structures 10, 70 a or 70 bconfigured as a pigment is that color can be blended according todesired specification. The color of the optical structure 10 can bedesigned by using computer software to calculate the thickness of thevarious layers of the optical structure 10, 70 a or 70 b that wouldprovide a desired reflection and/or transmission characteristics.Optical structures 10, 70 a or 70 b that can provide specific colors canbe designed using the computer software and then fabricated.Additionally, different color shifting optical structures 10, 70 a or 70b that produce different colors can be included together and/or colorshifting optical structures such as described herein can be combinedwith non-color shifting pigments or dyes to produce different colors.

The optical structure 10, 70 a or 70 b can be fabricated using a varietyof methods including but not limited to vacuum deposition, coatingmethods, etc. One method of fabrication of the optical structures 10described herein uses a vacuum coater that employs batch or rollcoating. In one method of fabricating the optical structure 10, a firsttransparent high index layer (e.g., layer 12 or layer 16 of FIG. 11) isdeposited onto carrier or base layer such as a sheet or web or othersubstrate. The carrier, web, base layer or substrate can comprisematerials such as, for example, polyester or a polyester with releasecharacteristics such that the optical structure can be readily separatedfrom the web or base layer. A release layer between the base layer andthe plurality of other optical layers the form the optical structure maybe used to permit separation of the optical layers comprising theoptical structure from the base layer or web. A first metal layer (e.g.,layer 13 or layer 15), a transparent dielectric layer comprising high orlow refractive index material (e.g., layer 14), a second metal layer(e.g., layer 15 or layer 13), and a second transparent high index layer(e.g., layer 16 or layer 12) is deposited over the first transparenthigh index layer in sequence (e.g., layer 12 or layer 16 of FIG. 11).The various layers can be deposited in sequence in some embodiments.However, in other embodiments, one or more intervening layers can bedisposed between any of the first metal layer, the transparentdielectric layer comprising high or low refractive index material, thesecond metal layer, and the second transparent high index layer. Asexamples, in some cases the transparent high index layers and thedielectric layer can be deposited using electron gun while the first andthe second metal layers can be deposited by using electron gun orsputtering.

Some materials, like ZnS or MgF₂, can be evaporated from a resistancesource. In instances wherein the transparent dielectric layer comprisinghigh or low refractive index material comprises a polymer, a processknown as PML (Polymer Multi-Layer) as described in U.S. Pat. No.5,877,895 can be used. The disclosure of U.S. Pat. No. 5,877,895 isincorporated by reference herein in its entirety.

Optical Structures Comprising Dielectric Layers Surrounded by MetalLayers (e.g., M/D/M/D/M Optical Stack)

FIG. 24A schematically illustrates an implementation of an opticalstructure 300 a comprising a stack of layers that can be used as asecurity feature. The optical structure 300 a comprises at least twodielectric layers 303 a and 303 b and at least three metal layers 301 a,301 b, and 301 c. In various implementations, the at least three metallayers 301 a, 301 b, and 301 c can comprise a material selected from agroup consisting of silver (Ag), silver alloys, gold (Au), and goldalloys. In some implementations, the at least three metal layers 301 a,301 b, and 301 c can comprise palladium (Pd). For example, the at leastthree metal layers 301 a, 301 b, and 301 c can comprise silver alloyswith palladium. The amount of palladium in some such implementations canbe less than or equal to about 10% by weight.

In various implementations, different metal layers (e.g. metal layers301 a, 301 b, and 301 c) can have a thickness in a range between about 3nm and about 120 nm. For example, the thickness of the different metallayers (e.g. metal layers 301 a, 301 b, and 301 c) can be greater thanor equal to about 3 nm and less than or equal to about 20 nm, greaterthan or equal to about 7.5 nm and less than or equal to about 25 nm,greater than or equal to about 10 nm and less than or equal to about27.5 nm, greater than or equal to about 12.5 nm and less than or equalto about 30 nm, greater than or equal to about 15 nm and less than orequal to about 35 nm, greater than or equal to about 17.5 nm and lessthan or equal to about 37.5 nm, greater than or equal to about 20 nm andless than or equal to about 40 nm, greater than or equal to about 25 nmand less than or equal to about 50 nm, greater than or equal to about 30nm and less than or equal to about 60 nm, greater than or equal to about35 nm and less than or equal to about 55 nm, greater than or equal toabout 45 nm and less than or equal to about 75 nm, greater than or equalto about 60 nm and less than or equal to about 80 nm, greater than orequal to about 75 nm and less than or equal to about 100 nm, greaterthan or equal to about 90 nm and less than about 120 nm, or anythickness in a range/sub-range defined by any of these values.

In various implementations, the different metal layers 301 a, 301 b and301 c can have the same thickness. However, in some implementations, thedifferent metal layers 301 a, 301 b and 301 c can have differentthickness. In some implementations, two of the three metal layers 301 a,301 b and 301 c have different thicknesses while in others all threemetal layers have different thicknesses. In some implementations, themetal layer 301 b can have a thickness greater than the thickness of themetal layer 301 a and/or metal layer 301 c. For example, the thicknessof the metal layer 301 b can be in a range between about 1.1 times andabout 2 times the thickness of the metal layer 301 a and/or the metallayer 301 c.

In various implementations, one or more of the metal layers 301 a, 301 band 301 c can be configured as a continuous layer. However, in someimplementations, one or more of the metal layers 301 a, 301 b and 301 ccan be discontinuous. Accordingly, any of the metal layers 301 a, 301 band 301 c can comprise separate regions comprising the metallic materialseparated by regions comprising a non-metallic material. For example,any of the metal layers 301 a, 301 b and 301 c can comprise one or moreislands comprising the metallic material spaced apart by regionscomprising dielectric material such as the dielectric material of one orboth of the layers 303 a and 303 b. In various implementations, one ormore of the metal layers 301 a, 301 b and 301 c need not be a continuouslayer or film. Instead, any of the metal layers 301 a, 301 b and 301 ccan be configured in the form of spheres or half-domes. In someimplementations, one or more of the metal layers 301 a, 301 b and 301 cconfigured in the form of spheres or half-domes can coalesce into acontinuous film during or following the fabrication process.

In various implementations, the different metal layers 301 a, 301 b, and301 c can have a ratio of the real part (n) of the refractive index ofthe different metal layers 301 a, 301 b, and 301 c to the imaginary part(k) of the refractive index that is greater than or equal to about 0.01and less than or equal to about 0.2. For example, the different metallayers 301 a, 301 b, and 301 c can comprise metals that have an n/kvalue between about 0.01 and about 0.2, between about 0.015 and about0.2, between about 0.01 and about 0.15, between about 0.01 and about0.1, between about 0.1 and about 0.2, or any value in a range orsub-range defined by any these values. As another example, the differentmetal layers 301 a, 301 b, and 301 c can comprise metals that have ann/k value of about 0.0166. As yet another example, the different metallayers 301 a, 301 b, and 301 c can comprise metals that have an n/kvalue of about 0.158.

The different dielectric layers 303 a and 303 b can have a thicknessbetween about 40 nm and about 850 nm. For example, the differentdielectric layers 303 a and 303 b can have a thickness greater than orequal to about 50 nm and less than or equal to about 800 nm, greaterthan or equal to about 75 nm and less than or equal to about 750 nm,greater than or equal to about 100 nm and less than or equal to about700 nm, greater than or equal to about 150 nm and less than or equal toabout 650 nm, greater than or equal to about 200 nm and less than orequal to about 600 nm, greater than or equal to about 250 nm and lessthan or equal to about 550 nm, greater than or equal to about 300 nm andless than or equal to about 500 nm, greater than or equal to about 350nm and less than or equal to about 450 nm, or a thickness having a valuein any range/sub-range defined by any of these values.

In various implementations, the different dielectric layers 303 a and303 b can have the same thickness. However, in some implementations, thedifferent dielectric layers 303 a and 303 b can have differentthickness. For example, the thickness of one of the dielectric layers303 a or 303 b can be in a range between about 1.5 times-10 times thethickness of another one of the dielectric layers 303 a or 303 b.

The different dielectric layers 303 a and 303 b can have a refractiveindex between about 1.38 and about 2.4. For example, the refractiveindex of the different dielectric layers 303 a and 303 b can be greaterthan or equal to about 1.38 and less than or equal to about 2.4, greaterthan or equal to about 1.5 and less than or equal to about 2.3, greaterthan or equal to about 1.6 and less than or equal to about 2.2, greaterthan or equal to about 1.7 and less than or equal to about 2.1, greaterthan or equal to about 1.8 and less than or equal to about 2.1, greaterthan or equal to about 1.9 and less than or equal to about 2.0, or anyvalues in a range/sub-range defined by any of these values.

The imaginary part (k) of the refractive index of the differentdielectric layers 303 a and 303 b can be sufficiently low such that thedifferent dielectric layers 303 a and 303 b are substantiallytransparent to light in the visible spectral range. For example theimaginary part (k) of the refractive index of the different dielectriclayers 303 a and 303 b can be equal to zero (0) or be close to zero (0).In various implementations, the imaginary part (k) of the refractiveindex of the different dielectric layers 303 a and 303 b can besufficiently low such that very little of the incident visible light isabsorbed by the different dielectric layers 303 a and 303 b. Forexample, in various implementations the composition and the thickness ofthe different dielectric layers 303 a and 303 b can be configured suchthat less than about 5% of the incident visible light is absorbed by thedifferent dielectric layers 303 a and 303 b. In various implementations,the different dielectric layers can comprise a material that is waterwhite.

In some implementations, the dielectric layers 303 a and 303 b cancomprise materials including but not limited to silicon dioxide (SiO₂),magnesium fluoride (MgF₂), zirconium dioxide (ZrO₂), ceric oxide (CeO₂),titanium dioxide (TiO₂), tantalum pentoxide (Ta₂O₅), yttrium oxide(Y₂O₃), indium oxide (In₂O₃), tin oxide (SnO₂), indium tin oxide (ITO),aluminum oxide (Al₂O₃), or tungsten trioxide (WO₃), organic polymerlayers or combinations thereof.

Various implementations of the optical structure 300 a can compriseoptional passivation layers (or protective layers or “flash” layers) 305a and 305 b disposed on a side of the metal layers 301 a and 301 c thatis opposite to the side facing the dielectric layers 303 a and 303 b.Metal surfaces can oxidize and/or corrode, which may affect opticalperformance. As an example, when exposed silver oxidizes and corrodes,silver sulfide can form and compromise optical performance. Finelydivided metal particles, particulates, or pieces may also spontaneouslycombust under the right conditions. For example, fires may occur in acoating machine when the machine is brought up to atmosphere. Explosionscan also occur during the milling process, e.g., when milling isperformed in air, using a cyclone type classifier. The passivationlayers 305 a and 305 b can provide protective layers to enhancedurability, potentially reduce or prevent oxidation and/or corrosion ofthe metal layers 301 a and 301 b, and allow possibly for saferprocessing.

Various embodiments of the optical structure 300 a can be configured asplatelets that are suspended in an ink medium to form a pigment. In somesuch embodiments, the passivation layers 305 a and 305 b can comprise amaterial having a refractive index that is matched (e.g., substantiallyequal or equal) to the refractive index of the ink medium. By choosingthe material of the passivation layers 305 a and 305 b to have arefractive index that is matched (e.g., substantially equal or equal) tothe refractive index of the ink medium, the passivation layers 305 a and305 b can be configured to reduce or prevent oxidation or corrosion ofthe metal layers 301 a and 301 b without affecting or substantiallyaffecting the overall optical properties of the optical structure 300 a.For example, silicon dioxide can be used to closely or substantiallyoptically match the ink medium (e.g., a medium comprising resin).Various implementations of the optical structure 300 a can be configuredas films, foils, threads, laminates, hot stamps, window patches, labels,etc. In some instances, the passivation layers 305 a and 305 b cancomprise a material having a high refractive index (e.g., greater thanor equal to about 1.65). In some implementations, zinc sulfide can beused outside of a non-shifting optical stack with negligible effect onthe optical performance in either reflection or transmission.

The passivation layers 305 a and 305 b can have a thickness in a rangefrom about 2 nm to about 500 nm. For example, the thickness of thepassivation layers 305 a and 305 b can be greater than or equal to about2 nm and less than or equal to about 10 nm, greater than or equal toabout 2 nm and less than or equal to about 20 nm, greater than or equalto about 5 nm and less than or equal to about 10 nm, greater than orequal to about 5 nm and less than or equal to about 20 nm, greater thanor equal to about 10 nm and less than or equal to about 20 nm, greaterthan or equal to about 20 nm and less than or equal to about 40 nm,greater than or equal to about 30 nm and less than or equal to about 50nm, greater than or equal to about 40 nm and less than or equal to about60 nm, greater than or equal to about 50 nm and less than or equal toabout 70 nm, greater than or equal to about 60 nm and less than or equalto about 80 nm, greater than or equal to about 70 nm and less than orequal to about 90 nm, greater than or equal to about 80 nm and less thanor equal to about 100 nm, greater than or equal to about 90 nm and lessthan or equal to about 110 nm, greater than or equal to about 100 nm andless than or equal to about 150 nm. greater than or equal to about 125nm and less than or equal to about 175 nm, greater than or equal toabout 150 nm and less than or equal to about 200 nm, greater than orequal to about 175 nm and less than or equal to about 225 nm, greaterthan or equal to about 200 nm and less than or equal to about 250 nm,greater than or equal to about 225 nm and less than or equal to about275 nm, greater than or equal to about 300 nm and less than or equal toabout 350 nm, greater than or equal to about 325 nm and less than orequal to about 375 nm, greater than or equal to about 350 nm and lessthan or equal to about 400 nm, greater than or equal to about 400 nm andless than or equal to about 450 nm, greater than or equal to about 450nm and less than or equal to about 500 nm, or any thickness in anyrange/sub-range defined by any of these values.

In some instances, the passivation layers 305 a and 305 b can comprise amaterial having a refractive index between about 1.45 and about 1.6. Forexample, the passivation layers 305 a and 305 b can comprise a materialhaving a refractive index greater than or equal to about 1.45 and lessthan or equal to about 1.55, greater than or equal to about 1.48 andless than or equal to about 1.57, greater than or equal to about 1.5 andless than or equal to about 1.58, greater than or equal to about 1.53and less than or equal to about 1.6, or any value in any range/sub-rangedefined by any of these values. In various implementations, thepassivation layers 305 a and 305 b can comprise silicon dioxide, atransparent dielectric material or a ultraviolet (UV) curable polymer.

In some instances, the passivation layers 305 a and 305 b can comprise amaterial having an refractive index greater than or equal to about 1.65.In various implementations, the passivation layers 305 a and 305 b cancomprise ZrO₂, TiO₂, ZnS, ITO (indium tin oxide), CeO₂ or Ta₂O₃.

Many implementations of the optical structure 300 a may comprise no morethan three metal layers 301 a, 301 b, and 301 c and no more than twodielectric layers 303 a and 303 b. For example, various implementationsof the optical structure 300 a may comprise exactly three metal layers301 a, 301 b, and 301 c and exactly two dielectric layers 303 a and 303b. Some such implementations of the optical structure 300 a can have athickness that is less than or equal to about 2.5 microns.

Fabricating the optical structure 300 a can include providing a firstlayer 303 a comprising dielectric material and depositing a layer ofmetal 301 b on one side of the first dielectric layer 303 a. A secondlayer 303 b comprising dielectric material can be disposed over themetal layer 301 b. A layer of metal 301 a can be further disposed overthe side of the first dielectric layer 303 a that is opposite the sideof the metal layer 301 b. A layer of metal 301 c can be further disposedover the side of the second dielectric layer 303 b that is opposite theside of the metal layer 301 b. The metal layers 301 a, 301 b, and 301 ccan be deposited as a continuous thin film, as small spheres, metallicclusters or island like structures. The first dielectric layer 303 a canbe disposed and/or formed over a support. The support is also referredto herein as a base layer. The support can comprise a carrier. Thesupport can comprise a sheet such as a web. The support can comprise asubstrate. The substrate can be a continuous sheet of PET, acrylate, orother polymeric web structure. The support can comprise a non-wovenfabric. Non-woven fabrics can be flat, porous sheets comprising fibers.In some implementations, the non-woven fabric can be configured as asheet or a web structure that is bonded together by entangling fiber orfilaments mechanically, thermally, or chemically. In someimplementations, the non-woven fabric can comprise perforated films. Insome implementations, the non-woven fabric can comprise synthetic fiberssuch as polypropylene or polyester or fiber glass.

The support can be coated with a release layer comprising a releaseagent. The release agent can be soluble in solvent or water. The releaselayer can be polyvinyl alcohol, which is water soluble or an acrylatewhich is soluble in a solvent. The release layer can comprise a coating,such as, for example, salt (NaCl) or cryolite (Na₃AlF₆) deposited byevaporation before the layers of the optical structure aredeposited/formed.

In some implementations using a support configured as a non-wovenfabric, the non-woven fabric can be coated with a release layer. Suchimplementations can be dipped or immersed in a solvent or water thatacts as a release agent to dissolve or remove the release layer. Therelease agent (e.g., the solvent or water) is configured to penetratefrom a side of the non-woven fabric opposite the side on which theoptical structure is disposed to facilitate release of the opticalstructure instead of having to penetrate through the optical structure.

One method of fabricating the optical structure 300 a shown in FIG. 24Autilizes a vacuum roll coater. In this method, the optical structure 300a is fabricated by depositing the metallic and dielectric materials ofthe various layers on a web using vacuum deposition methods, such as,for example, electron beam (e-beam) deposition, sputtering and/orresistive heating. The web can comprise a polymeric material, such asfor example polyethylene terephthalate (PET) or acrylate. If the opticalstructure is configured to be used as a foil or a film, then the variouslayers of the optical structure 300 a can be deposited directly on asurface of the web. However, in other implementations, a release coatingcan be applied to the surface of the web prior to the vacuum depositionof the various layers. For example, if the optical structure 300 a isconfigured to be used as a pigment, then the optical structure can beapplied on the release coating. In some implementations, the variouslayers of the optical stack 300 a can be deposited in series. Forexample, in certain implementations, the metal layer 301 c can bedeposited first followed by the dielectric layer 303 b, followed by themetal layer 301 b, followed by the dielectric layer 303 a, followed bythe metal layer 301 a. In various implementations of the opticalstructure can include the passivation layers 305 a and 305 b, forexample, the passivation layer 305 b can be deposited prior to thedeposition metal layer 301 c and the passivation layer 305 a can bedeposited over the metal layer 301 a.

In some implementations, the optical structure 300 a fabricated usingthe vacuum roll coater can be released from the web by immersing the webcomprising the release layer and the deposited optical structure in abath of a solvent comprising salt (NaCl) or cryolite (Na₃AlF₆) to removeor dissolve the release layer and release the optical structure 300 a.In some cases, the optical structure 300 a can break or shatter inpieces having various shapes and sizes when released from the web. Thesolvent can be removed and the various pieces of the optical structure300 a can be dried and subsequently milled to form platelets havingdesired size and thickness for use as a pigment (e.g., in Intaglio ink).

FIG. 24B illustrates a cross-sectional view of an implementation of anoptical structure 300 b including a first region 310 comprising a firstmetallic material which is surrounded by a second region 312 comprisinga dielectric material. The second region 312 comprising the dielectricmaterial can be surrounded by a third region 314 comprising a secondmetallic material. The third region 314 can be optionally surrounded bya fourth region 316 comprising a dielectric material having a refractiveindex between about 1.45 and about 1.6 configured as a passivationregion to reduce or prevent oxidation of the second metallic material.Such a structure can be considered to have three metal layers, twodielectric layers and two optional passivation layers as noted from thecross-sectional view shown in FIG. 24B. The optical structure 300 b canbe fabricated by providing a substrate comprising the first metallicmaterial and disposing the dielectric material on the exposed surfacesof the substrate using physical and/or chemical deposition methods. Theexposed surfaces of the dielectric material can be covered by the secondmetallic material using physical and/or chemical deposition methods. Forexample, the optical structure 300 b can be fabricated using variousmethods described in U.S. Pat. No. 6,524,381 which is incorporatedherein by reference in its entirety.

The chemical composition and various physical characteristics (e.g.,thickness) of the first region 310 can be similar to the chemicalcomposition and various physical characteristics (e.g., thickness) ofthe metal layer 301 b discussed above. The chemical composition andvarious physical characteristics (e.g., thickness) of the second region312 can be similar to the chemical composition and various physicalcharacteristics (e.g., thickness) of the dielectric layers 303 a and 303b discussed above. The chemical composition and various physicalcharacteristics (e.g., thickness) of the third region 314 can be similarto the chemical composition and various physical characteristics (e.g.,thickness) of the metal layers 301 a and 301 c discussed above. Thechemical composition and various physical characteristics (e.g.,thickness) of the fourth region 316 can be similar to the chemicalcomposition and various physical characteristics (e.g., thickness) ofthe passivation layers 305 a and 305 b discussed above.

Accordingly, in various implementations, the first region 310 cancomprise silver, silver alloys, gold and/or gold alloys. The thicknessof the first region 310 can be between about 3 nm and about 100 nm. Thesecond region 312 can comprise materials including but not limited tosilicon dioxide (SiO₂), magnesium fluoride (MgF₂), zirconium dioxide(ZrO₂), ceric oxide (CeO₂), titanium dioxide (TiO₂), tantalum pentoxide(Ta₂O₅), yttrium oxide (Y₂O₃), indium oxide (In₂O₃), tin oxide (SnO₂),indium tin oxide (ITO), aluminum oxide (Al₂O₃), or tungsten trioxide(WO₃), or organic polymer layers. or combinations thereof. The secondregion 312 can extend to a height between about 50 nm and 800 nm from anoutermost surface of the first region 310. The third region 314 cancomprise silver, silver alloys, gold and/or gold alloys and extend to aheight between about 3 nm and about 100 nm from an outermost surface ofthe first region 310. The fourth region 316 can comprise a dielectricmaterial having a refractive index between about 1.45 and about 1.6 andextend to a height between about 10 nm and about 100 nm from anoutermost surface of the third region 314.

In various implementations, the first region 310 can be configured as aslab, flake, a sphere, spheroid, ellipsoid, disc, or any other3-dimensional shape enclosing a volume. The first region 310 may have aregular or irregular shape. For example, as shown in FIG. 24B, the firstregion 310 can be configured as a slab (e.g., a slab having nanometerscale thickness and micrometer scale lateral dimensions) having twomajor surfaces and one or more edge surfaces disposed between the twomajor surfaces. In some implementations, a number of edge surfaces maybe disposed between the two major surfaces of the slab. The number ofedge surfaces may, for example, be one, two, three, four, five, six,seven, eight, nine, ten, twelve, twenty, thirty, fifty, etc. or in anyrange between any of these values. Values outside these ranges are alsopossible. The major surfaces of the slab can have a variety of shapes.For example, one or both of the major surfaces 310 a and 310 b can havea rectilinear or curvilinear shape in certain implementations. The shapemay be regular or irregular in certain implementations. For example, oneor both of the major surfaces can have a square shape, a rectangularshape, a circular shape, an oval shape, an elliptical shape, pentagonalshape, a hexagonal shape, an octagonal shape or any polygonal shape. Invarious implementations, one or both of the major surface can havejagged edges such that the lateral dimensions (e.g., length or width) ofthe one or both of the major surface varies across the area of the oneor both of the major surface. Other configurations are also possible.Additionally, other shapes are also possible. One or more of the edgesurfaces can have a variety of shapes (e.g., as viewed from the side),such as, for example, a square shape, a rectangular shape, an ovalshape, an elliptical shape, a pentagonal shape, a hexagonal shape, anoctagonal shape or any a polygonal shape.

The shape of the one or more of the edge surfaces (e.g., as viewed fromthe side) can be rectilinear or curvilinear in certain implementations.The shape may be regular or irregular in certain implementations.Similarly, the cross-section through the first region 310 parallel toone of the major surfaces, can be rectilinear or curvilinear in certainimplementations and can be regular or irregular in certainimplementations. For example, the cross-section can have a square shape,a rectangular shape, a circular shape, an oval shape, an ellipticalshape, pentagonal shape, a hexagonal shape, an octagonal shape or any apolygonal shape. Other shapes are also possible. Likewise, thecross-section through the first region 310 perpendicular to one of themajor surfaces, can be rectilinear or curvilinear in certainimplementations and can be regular or irregular implementations. Forexample, the cross-section can have a square shape, a rectangular shape,a circular shape, an oval shape, an elliptical shape, pentagonal shape,a hexagonal shape, an octagonal shape or any a polygonal shape. Othershapes are also possible. In various implementations, an area, a lengthand/or a width of the major surfaces of the first region 310 can begreater than or equal to about 2, 3, 4, 5, 6, 8, or 10 times thethickness of the first region 310 and less than or equal to about 50times the thickness of the first region 310, or any value in arange/sub-range between any of these values. Accordingly, the firstregion 310 can have a large aspect ratio. Other sizes and shapes,however, are possible.

The optical structure 300 a and 300 b can be configured as a film or afoil by disposing over a substrate or other support layer having athickness, for example, greater than or equal to about 10 microns andless than or equal to about 25 microns. For example, a substrate orsupport layer can have a thickness greater than or equal to 12 micronsand less than or equal to 22.5 microns, greater than or equal to 15microns and less than or equal to about 20 microns. The substrate orsupport layer can comprise materials, such as, for example, polyethyleneterephthalate (PET), acrylate, polyester, polyethylene, polypropylene,or polycarbonate. The support or support layer itself can bedissolvable. The support or support layer, for example, can alsocomprise polyvinyl alcohol, which can be dissolved, for example, inwater. Accordingly, instead of using a release layer on a insolublesupport web, the support web itself may comprise soluble material.Accordingly, the support or support layer can be dissolved leaving theoptical coating remaining. The optical structure 300 a configured as afilm or a foil can be encapsulated with a polymer, such as, for examplea UV cured polymer.

Instead of a film or a foil, the optical structure 300 a or 300 b can bedivided into platelets having a size that is suitable for a pigment orprinting ink. Platelets having a size that is suitable for a pigment orprinting ink can have an length, and/or width that is about 5-10 times,10-20 times or 30-40 times the thickness of the platelet, in someimplementations. Accordingly, the platelets can have a thickness ofabout 1 micron, and/or can have a width and/or a length that is betweenapproximately 5 micron and about 50 microns. For example, the widthand/or a length can be greater than or equal to about 5 micron and lessthan or equal to about 15 microns, greater than or equal to about 5microns and less than or equal to about 10 microns, greater than orequal to about 5 micron and less than or equal to about 40 microns,greater than or equal to about 5 microns and less than or equal to about20 microns, or any value in the ranges/sub-ranges defined by thesevalues. Platelets having a length and/or width that is less than about5-10 times the thickness of the platelet, such as, for example having alength and/or width that is equal to the thickness of the platelet canbe oriented along their edges in the printing ink or pigment. This canbe disadvantageous in some implementations since pigment or printing inkcomprising platelets that are oriented along their edges may not exhibitthe desired colors in reflection and transmission modes. Dimensions suchas, thicknesses, lengths and/or widths outside these ranges, however,are also possible.

In some implementations, the optical structure 300 a or 300 b can befractured, cut, diced or otherwise separated to obtain the separate, forexample, pieces or platelets. These pieces or platelets can have micronscale sizes in certain embodiments. In some implementations, theobtained platelets may be surrounded by an encapsulating layer similarto the encapsulating layer 21 discussed above. For example, the opticalstructures 300 a and 300 b including the passivation layers 305 a and305 b can further comprise an encapsulating layer similar to theencapsulating layer 21 discussed above. In some implementations, theencapsulating layer can comprise a moisture resistant material, such as,for example silicon dioxide. The encapsulating layer can also comprisesilica spheres similar to silica spheres 22 and 23 discussed above. Theencapsulating layer can additionally and/or alternatively reduce theoccurrence of delamination of the different layers of the opticalstructure 300 a/300 b. The optical structures 300 a/300 b with thesurrounding encapsulating layer, which may potentially comprise thesilica spheres, can be configured as platelets that are suitable for apigment or printing ink. The silica spheres of the encapsulating layercan help prevent the platelets from adhering to one another. Forexample, in some cases, without the spheres the platelets may sticktogether. The silica spheres can also prevent or reduce the likelihoodof the platelets sticking to the print rollers in the printing machine.One method of surrounding the optical structure 300 a/300 b with theencapsulating layer comprising silica spheres can rely on sol-geltechnology using tetraethylorthosilicate (TEOS) discussed above. Otherprocesses, however, may be employed.

The pigment can be formed by a plurality of optical structures 300 a/300b configured as platelets. Such a pigment may be color shifting (e.g.,the color reflected and/or transmitted changes with angle of view orangle of incidence of light), in some cases. In some embodiments,non-color shifting pigment or dye may be mixed with the pigment. In someembodiments other materials may be included with the plurality ofoptical structures 300 a/300 b configured as platelets to form thepigment. Although some of the resultant pigments discussed herein canprovide color shift with change in viewing angle or angle of incidenceof light, pigments that do not exhibit color shift with change inviewing angle or angle of incidence of light or that produce very littlecolor shift with change in viewing angle or angle of incidence of lightare also contemplated.

In some embodiments, the plurality of optical structures 300 a/300 bconfigured as platelets can be added to a medium such as a polymer(e.g., a polymeric resin) to form a dichroic ink, a pigment, or paint asdiscussed above with reference to FIG. 12B-1. In some implementations,the medium can be an organic resin. The refractive index of the mediumcan be in a range between about 1.4 and about 1.6 (e.g. 1.5). The mediumcan comprise an optical material that is substantially clear. The mediumcan be substantially transparent to visible light. The platelets can besuspended in the medium (e.g., polymer). The platelets can be randomlyoriented in the medium (e.g., polymer) as discussed above with referenceto FIG. 12B-1. During the printing process, in some cases, theindividual platelets (e.g., the majority of the platelets) can beoriented parallel to the surface of the object (e.g., paper) to whichthe pigment, the paint, or the dichroic ink is being applied as a resultof, for example, the printing action, gravity, and/or surface tension ofthe normal drying process of the pigment, the paint, or the dichroic inkas discussed above with reference to FIG. 12B-2. The medium can comprisematerial including but not limited to acrylic melamine, urethanes,polyesters, vinyl resins, acrylates, methacrylate, ABS resins, epoxies,styrenes and formulations based on alkyd resins and mixtures thereof. Insome implementations, the passivation layer 305 a and 305 b, theencapsulating layer and/or the silica balls can have a refractive indexthat closely matches the refractive index of the medium, e.g., polymer,in which the optical structures 300 a/300 b configured as platelets aresuspended such that the passivation layers 305 a/305 b, theencapsulating layer and/or the silica balls do not adversely affect theoptical performance of the pigment, the paint, or the dichroic ink inthe medium.

In various implementations, the optical structures 300 a/300 bconfigured as platelets need not be surrounded by an encapsulatinglayer. In such implementations, one or more platelets that are notencapsulated by an encapsulating layer can be added or mixed with an inkor a pigment medium (e.g., varnish, polymeric resin, etc.) to obtain adichroic ink or pigment as discussed above. In various implementations,the dichroic ink or pigment can comprise a plurality of platelets. Theoptical structures 300 a/300 b that are configured as the plurality ofplatelets can have different distributions of shapes, sizes, thicknessesand/or aspect ratios. The optical structures 300 a/300 b that areconfigured as the plurality of platelets can also have different opticalproperties. For example, the optical structures 300 a/300 b that areconfigured as the plurality of platelets can also have different colorproperties.

In various implementations, a silane coupling agent can be bonded to theencapsulating layer of the optical structures 300 a/300 b as discussedabove with reference to FIG. 13. As discussed above, bonding of thesilane coupling agent to the encapsulating layer can occur through ahydrolyzing reaction. The silane coupling agent can bind to the polymer(e.g., polymeric resin) of the printing ink or paint medium so that theheterogeneous mixture of pigment and the polymer do not separate duringthe printing process and substantially function in much the same way asa homogeneous medium would function. The printing ink or paint mediumcan comprise material including but not limited to acrylic melamine,urethanes, polyesters, vinyl resins, acrylates, methacrylate, ABSresins, epoxies, styrenes and formulations based on alkyd resins andmixtures thereof. The silane coupling agents used can be similar to thesilane coupling agents sold by Gelest Company (Morristown, Pa. USA). Insome implementations, the silane coupling agent can comprise ahydrolyzable group, such as, for example, an alkoxy, an acyloxy, ahalogen or an amine. Following a hydrolyzing reaction (e.g.,hydrolysis), a reactive silanol group is formed, which can condense withother silanol groups, for example, with the silica spheres of theencapsulating layer or the encapsulating layer of silica to formsiloxane linkages. The other end of the silane coupling agent comprisesthe R-group. The R-group can comprise various reactive compoundsincluding but not limited to compounds with double bonds, isocyanate oramino acid moieties. Reaction of the double bond via free radicalchemistry can form bonds with the ink polymer(s) such as those based onacrylates, methacrylates or polyesters based resins. For example,isocyanate functional silanes, alkanolamine functional silanes andaminosilanes can form urethane linkages.

Without any loss of generality, in various implementations of theoptical structure 300 a/300 b configured as a platelet that do notcomprise the encapsulating layer, the silane coupling agent can bebonded to one or both of the passivation layers 305 a/305 b comprising adielectric material (e.g., TiO₂) suitable to be bonded with the silanecoupling agent.

An ink comprising various implementations of the optical structure 300a/300 b configured as platelets can be applied to a substrate (e.g., apolyester web) and dried. In some implementations, the substratecomprising the ink can be cut in strips to form a security thread havingthe optical characteristics of the various implementations of theoptical structure 300 a/300 b. For example, depending on the thicknessand composition of the various layers of the various implementations ofthe optical structure 300 a/300 b included in the ink, the ink canproduce a color in transmission mode and a different color in reflectionmode. As discussed above, in some implementations, the color in thetransmission mode can be a complementary color of the color in thereflection mode. Additionally, in some implementations, the color in thetransmission mode and the reflection mode can vary with viewing angle.The security thread can be integrated with products and/or packaging toimprove security of the products and/or packaging. In someimplementations, the substrate comprising the ink including variousimplementations of the optical structure 300 a/300 b can be configuredas a laminate and adhered to a security document (e.g., a banknote). Insome implementations, the ink comprising various implementations of theoptical structure 300 a/300 b applied to a releasable carrier web can beconfigured as a hot stamp having the optical characteristics of thevarious implementations of the optical structure 300 a/300 b.

Without any loss of generality, the optical structure 300 a/300 b can beconsidered as an interference stack or cavity. Ambient light incident onthe surface of the optical structure 300 a/300 b is partially reflectedfrom the various layers of the optical structure 300 a/300 b andpartially transmitted through the various layers of the opticalstructure 300 a/300 b. Some wavelengths of the ambient light reflectedfrom the various layers may interfere constructively and some otherwavelengths of the ambient light reflected from the various layers mayinterfere destructively. Similarly, some wavelengths of lighttransmitted through the various layers may interfere constructively andsome other wavelengths of the ambient light transmitted through thevarious layers may interfere destructively. As a result of which, theoptical structure 300 a/300 b appears colored when viewed intransmission and reflection mode. In general, the color and theintensity of light reflected by and transmitted through the opticalstructure 300 a/300 b can depend on the thickness and the material ofthe various layers of the optical structure 300 a/300 b. By changing thematerial and the thickness of the various layers, the color andintensity of light reflected by and transmitted through the opticalstructure 300 a/300 b can be varied.

Without subscribing to any particular scientific theory about theoperation of the optical structures 300 a/300 b, in general, thematerial and the thickness of the various layers can be configured suchthat some or all of the ambient light reflected by the various layersinterfere such that a node in the field occurs at one or more of thethree metal layers 301 a, 301 b, and 301 c for some of the wavelengthsof the ambient light. For example, some or all of the ambient lightreflected by the various layers interfere such that a node in the fieldoccurs at all the three metal layers 301 a, 301 b, and 301 c for some ofthe wavelengths of the ambient light. Again, without subscribing to aparticular scientific theory, based on the thickness of the three metallayers 301 a, 301 b, and 301 c and the dielectric layers 303 a and 303b, a portion of the incident light may be transmitted through theoptical structure 300 a/300 b as a result of the phenomenon of “inducedtransmittance” or “induced transmission”. The reflection andtransmission spectral characteristics are discussed below.

FIG. 25A is a CIE 1931 color space chromaticity diagram showing the xand y chromaticity coordinates of light transmitted through a firstexample of the optical structure 300 a or 300 b for different viewingangles between 0 degrees and 40 degrees with respect to a normal to asurface of the optical structure 300 a or 300 b. FIG. 25B is a CIE 1931color space chromaticity diagram showing the x and y chromaticitycoordinates of light reflected from the first example of the opticalstructure 300 a or 300 b for different viewing angles between 0 degreesand 40 degrees with respect to a normal to a surface of the opticalstructure 300 a or 300 b. The first example of the optical structure 300a or 300 b comprises a layer of silver (Ag) (corresponding to the layer301 b of FIG. 24A or the region 310 of FIG. 24B) having a thickness ofabout 100 nm surrounded by two layers of a dielectric materialcomprising zinc sulfide (ZnS) (corresponding to the layers 303 a and 303b of FIG. 24A or the region 312 of FIG. 24B) having an individualthickness of about 66 nm. The first example further comprises twoadditional silver layers disposed over the two dielectric layers(corresponding to the layers 301 a and 301 c of FIG. 24A or the region314 of FIG. 24B) having an individual thickness of about 50 nm. Toobtain the chromaticity of x and y chromaticity coordinates of lightreflected from and transmitted through the first example of the opticalstructure 300 a or 300 b, the optical structure 300 a or 300 b isencapsulated in a SiO₂ matrix, which is used to simulate the printingmedium or ink which has a similar refractive index.

As noted from FIGS. 25A and 25B, the first example of the opticalstructure 300 a or 300 b appears in different shades of green whenviewed in the transmission mode at different viewing angles between 0degrees and 40 degrees with respect to a normal to a surface of theoptical structure 300 a or 300 b and appears greyish purple when viewedin the reflection mode at different viewing angles between 0 degrees and40 degrees with respect to a normal to a surface of the opticalstructure 300 a or 300 b. The color in the transmission mode and thecolor in the reflection mode are complementary to each other. It isobserved from FIG. 25B that the color in the reflection mode does notvary significantly when viewed in the reflection mode at differentviewing angles between 0 degrees and 40 degrees with respect to a normalto a surface of the optical structure 300 a or 300 b. It is observedfrom FIG. 25A that there is a slight variation of the color in thetransmission mode when viewed in the transmission mode at differentviewing angles between 0 degrees and 40 degrees with respect to a normalto a surface of the optical structure 300 a or 300 b.

FIG. 25C illustrates the a*b* values in the CIE L*a*b* color space whenthe first example of the optical structure 300 a/300 b is viewed in thetransmission mode at different viewing angles between 0 degrees and 40degrees with respect to the normal to the surface of the first exampleof the optical structure 300 a/300 b. As the viewing angle increases thecolor of the first example of the optical structure 300 a/300 b in thetransmission mode shifts in the direction of the arrow 1501. Forexample, the color of the first example in the transmission mode canhave a lightness (L*) value between approximately 12.5 and approximately17.0 for different viewing angles between 0 degrees and 40 degrees withrespect to the normal to the surface of the first example of the opticalstructure 300 a/300 b. The color of the first example in thetransmission mode can have an (a*) value between approximately −44.5 andapproximately −51.5 for different viewing angles between 0 degrees and40 degrees with respect to the normal to the surface of the firstexample of the optical structure 300 a/300 b. The color of the firstexample in the transmission mode can have a (b*) value betweenapproximately 20.5 and approximately 27.0 for different viewing anglesbetween 0 degrees and 40 degrees with respect to the normal to thesurface of the first example of the optical structure 300 a/300 b.

FIG. 25D illustrates the a*b* values in the CIE L*a*b* color space whenthe first example of the optical structure 300 a/300 b is viewed in thereflection mode at different viewing angles between 0 degrees and 40degrees with respect to the normal to the surface of the first exampleof the optical structure 300 a/300 b. It is noted that as the viewingangle increases the color of the first example of the optical structure300 a/300 b in the reflection mode does not shift significantly. Thecolor of the first example in the reflection mode can have a lightness(L*) value between approximately 92.7 and approximately 92.8 fordifferent viewing angles between 0 degrees and 40 degrees with respectto the normal to the surface of the first example of the opticalstructure 300 a/300 b. The color of the first example in the reflectionmode can have an (a*) value between approximately 18.0 and approximately19.1 for different viewing angles between 0 degrees and 40 degrees withrespect to the normal to the surface of the first example of the opticalstructure 300 a/300 b. The color of the first example in the reflectionmode can have a (b*) value between approximately −8.7 and approximately−9.9 for different viewing angles between 0 degrees and 40 degrees withrespect to the normal to the surface of the first example of the opticalstructure 300 a/300 b.

FIG. 26A is a CIE 1931 color space chromaticity diagram showing the xand y chromaticity coordinates of light transmitted through a secondexample of the optical structure 300 a or 300 b for different viewingangles between 0 degrees and 40 degrees with respect to a normal to asurface of the optical structure 300 a or 300 b. FIG. 26B is a CIE 1931color space chromaticity diagram showing the x and y chromaticitycoordinates of light reflected from the second example of the opticalstructure 300 a or 300 b for different viewing angles between 0 degreesand 40 degrees with respect to a normal to a surface of the opticalstructure 300 a or 300 b. The second example of the optical structure300 a or 300 b comprises a layer of silver (Ag) (corresponding to thelayer 301 b of FIG. 24A or the region 310 of FIG. 24B) having athickness of about 10 nm surrounded by two layers of a dielectricmaterial comprising zinc sulfide (ZnS) (corresponding to the layers 303a and 303 b of FIG. 24A or the region 312 of FIG. 24B) having anindividual thickness of about 66 nm. The second example furthercomprises two additional silver layers disposed over the two dielectriclayers (corresponding to the layers 301 a and 301 c of FIG. 24A or theregion 314 of FIG. 24B) having an individual thickness of about 5 nm. Toobtain the chromaticity of x and y chromaticity coordinates of lightreflected from and transmitted through the second example of the opticalstructure 300 a or 300 b, the optical structure 300 a or 300 b isencapsulated in a SiO₂ matrix which is used to simulate the printingmedium or ink which has a similar refractive index.

As noted from FIGS. 26A and 26B, the second example of the opticalstructure 300 a or 300 b appears greenish grey when viewed in thetransmission mode at different viewing angles between 0 degrees and 40degrees with respect to a normal to a surface of the optical structure300 a or 300 b and appears blue or deep purple when viewed in thereflection mode at different viewing angles between 0 degrees and 40degrees with respect to a normal to a surface of the optical structure300 a or 300 b.

FIG. 26C illustrates the a*b* values in the CIE L*a*b* color space whenthe second example of the optical structure 300 a/300 b is viewed in thetransmission mode at different viewing angles between 0 degrees and 40degrees with respect to the normal to the surface of the second exampleof the optical structure 300 a/300 b. As the viewing angle increases thecolor of the second example of the optical structure 300 a/300 b in thetransmission mode shifts in the direction of the arrow 1601. The colorof the second example in the transmission mode can have a lightness (L*)value between approximately 96.0 and approximately 98.5 for differentviewing angles between 0 degrees and 40 degrees with respect to thenormal to the surface of the second example of the optical structure 300a/300 b. The color of the second example in the transmission mode canhave an (a*) value between approximately −6.2 and approximately −9.0 fordifferent viewing angles between 0 degrees and 40 degrees with respectto the normal to the surface of the second example of the opticalstructure 300 a/300 b. The color of the second example in thetransmission mode can have a (b*) value between approximately 12.9 andapproximately 25.7 for different viewing angles between 0 degrees and 40degrees with respect to the normal to the surface of the second exampleof the optical structure 300 a/300 b.

FIG. 26D illustrates the a*b* values in the CIE L*a*b* color space whenthe second example of the optical structure 300 a/300 b is viewed in thereflection mode at different viewing angles between 0 degrees and 40degrees with respect to the normal to the surface of the second exampleof the optical structure 300 a/300 b. As the viewing angle increases thecolor of the second example of the optical structure 300 a/300 b in thereflection mode shifts in the direction of the arrow 1603. The color ofthe second example in the reflection mode can have a lightness (L*)value between approximately 11.0 and approximately 26.5 for differentviewing angles between 0 degrees and 40 degrees with respect to thenormal to the surface of the second example of the optical structure 300a/300 b. The color of the second example in the reflection mode can havean (a*) value between approximately 44.5 and approximately 63.8 fordifferent viewing angles between 0 degrees and 40 degrees with respectto the normal to the surface of the second example of the opticalstructure 300 a/300 b. The color of the second example in the reflectionmode can have a (b*) value between approximately −69.0 and approximately−72.0 for different viewing angles between 0 degrees and 40 degrees withrespect to the normal to the surface of the second example of theoptical structure 300 a/300 b.

FIG. 27A shows the variation of the transmittance with wavelength for athird example of the optical structure 300 a/300 b at a viewing angle of0 degrees with respect to a normal to the surface of the opticalstructure 300 a/300 b. FIG. 27B shows the variation of the reflectancewith wavelength for the third example of the optical structure 300 a/300b at a viewing angle of 0 degrees with respect to a normal to thesurface of the optical structure 300 a/300 b. The third example of theoptical structure 300 a or 300 b comprises a layer of silver (Ag)(corresponding to the layer 301 b of FIG. 24A or the region 310 of FIG.24B) having a thickness of about 40 nm surrounded by two layers of adielectric material comprising magnesium fluoride (MgF₂) (correspondingto the layers 303 a and 303 b of FIG. 24A or the region 312 of FIG. 24B)having an individual thickness of about 185 nm. The third examplefurther comprises two additional silver layers disposed over the twodielectric layers (corresponding to the layers 301 a and 301 c of FIG.24A or the region 314 of FIG. 24B) having an individual thickness ofabout 23 nm. The third example of the optical structure 300 a or 300 bis encapsulated in a SiO₂ matrix which is used to simulate the printingmedium or ink which has a similar refractive index.

It is observed from FIG. 27A that the transmittance through the thirdexample of the optical structure 300 a/300 b is less than 10% in awavelength range between about 400 nm and about 600 nm. Thetransmittance is greater than about 10% for wavelengths greater thanabout 600 nm and less than about 700 nm. The maximum value of thetransmittance occurs at a wavelength between about 630 nm and about 650nm. It is observed from FIG. 27B that the reflectance from the thirdexample of the optical structure 300 a/300 b is less than 30% forwavelengths between about 630 nm and about 680 nm. It is observed fromthe transmittance and the reflectance spectra that the third example ofthe optical structure 300 a/300 b will appear red/orange in thetransmission mode and grey/blue in the reflection mode.

FIG. 27C is a CIE 1931 color space chromaticity diagram showing the xand y chromaticity coordinates of light transmitted through the thirdexample of the optical structure 300 a or 300 b for different viewingangles between 0 degrees and 40 degrees with respect to a normal to asurface of the optical structure 300 a or 300 b. As the viewing angleincreases, the color of the optical structure 300 a or 300 b changesfrom red towards green in the direction of the arrow 1701. FIG. 27Dillustrates the a*b* values in the CIE L*a*b* color space when the thirdexample of the optical structure 300 a/300 b is viewed in thetransmission mode at different viewing angles between 0 degrees and 40degrees with respect to the normal to the surface of the third exampleof the optical structure 300 a/300 b. As the viewing angle increases thecolor of the third example of the optical structure 300 a/300 b in thetransmission mode shifts in the direction of the arrow 1703. The colorof the third example in the transmission mode can have a lightness (L*)value between approximately 26.8 and approximately 77.2 for differentviewing angles between 0 degrees and 40 degrees with respect to thenormal to the surface of the third example of the optical structure 300a/300 b. The color of the third example in the transmission mode canhave an (a*) value between approximately −19.2 and approximately 66.0for different viewing angles between 0 degrees and 40 degrees withrespect to the normal to the surface of the third example of the opticalstructure 300 a/300 b. The color of the third example in thetransmission mode can have a (b*) value between approximately 35.9 andapproximately 98.8 for different viewing angles between 0 degrees and 40degrees with respect to the normal to the surface of the third exampleof the optical structure 300 a/300 b.

FIG. 27E is a CIE 1931 color space chromaticity diagram showing the xand y chromaticity coordinates of light reflected from the third exampleof the optical structure 300 a or 300 b for different viewing anglesbetween 0 degrees and 40 degrees with respect to a normal to a surfaceof the third example of the optical structure 300 a or 300 b. As theviewing angle increases, the color of the optical structure 300 a or 300b changes from grey towards blue in the direction of the arrow 1705.FIG. 27F illustrates the a*b* values in the CIE L*a*b* color space whenthe third example of the optical structure 300 a/300 b is viewed in thereflection mode at different viewing angles between 0 degrees and 40degrees with respect to the normal to the surface of the third exampleof the optical structure 300 a/300 b. As the viewing angle increases thecolor of the third example of the optical structure 300 a/300 b in thereflection mode shifts in the direction of the arrow 1707. The color ofthe third example in the reflection mode can have a lightness (L*) valuebetween approximately 63.3 and approximately 97.2 for different viewingangles between 0 degrees and 40 degrees with respect to the normal tothe surface of the third example of the optical structure 300 a/300 b.The color of the third example in the reflection mode can have an (a*)value between approximately −48.0 and approximately 15.5 for differentviewing angles between 0 degrees and 40 degrees with respect to thenormal to the surface of the third example of the optical structure 300a/300 b. The color of the third example in the reflection mode can havea (b*) value between approximately −1.0 and approximately −57.9 fordifferent viewing angles between 0 degrees and 40 degrees with respectto the normal to the surface of the third example of the opticalstructure 300 a/300 b.

FIG. 28A shows the variation of the transmittance with wavelength for afourth example of the optical structure 300 a/300 b at a viewing angleof 0 degrees with respect to a normal to the surface of the opticalstructure 300 a/300 b. FIG. 28B shows the variation of the reflectancewith wavelength for the fourth example of the optical structure 300a/300 b at a viewing angle of 0 degrees with respect to a normal to thesurface of the optical structure 300 a/300 b. The fourth example of theoptical structure 300 a or 300 b comprises a layer of gold (Au)(corresponding to the layer 301 b of FIG. 24A or the region 310 of FIG.24B) having a thickness of about 40 nm surrounded by two layers of adielectric material comprising magnesium fluoride (MgF₂) (correspondingto the layers 303 a and 303 b of FIG. 24A or the region 312 of FIG. 24B)having an individual thickness of about 185 nm. The fourth examplefurther comprises two additional gold layers disposed over the twodielectric layers (corresponding to the layers 301 a and 301 c of FIG.24A or the region 314 of FIG. 24B) having an individual thickness ofabout 23 nm. The fourth example of the optical structure 300 a or 300 bis encapsulated in a SiO₂ matrix which is used to simulate the printingmedium or ink which has a similar refractive index.

It is observed from FIG. 28A that the transmittance through the fourthexample of the optical structure 300 a/300 b is less than 10% in awavelength range between about 400 nm and about 600 nm. Thetransmittance is greater than about 10% for wavelengths greater thanabout 600 nm and less than about 700 nm. The maximum value of thetransmittance occurs at a wavelength between about 650 nm and about 675nm. It is observed from FIG. 28B that the reflectance from the fourthexample of the optical structure 300 a/300 b is greater than 30% forwavelengths between about 480 nm and about 650 nm. It is observed fromthe transmittance and the reflectance spectra that the fourth example ofthe optical structure 300 a/300 b will appear red/orange in thetransmission mode and yellow-green/aquamarine in the reflection mode.

FIG. 28C is a CIE 1931 color space chromaticity diagram showing the xand y chromaticity coordinates of light transmitted through the fourthexample of the optical structure 300 a or 300 b for different viewingangles between 0 degrees and 40 degrees with respect to a normal to asurface of the optical structure 300 a or 300 b. As the viewing angleincreases, the color of the optical structure 300 a or 300 b changesfrom red towards orange in the direction of the arrow 1801. FIG. 28Dillustrates the a*b* values in the CIE L*a*b* color space when thefourth example of the optical structure 300 a/300 b is viewed in thetransmission mode at different viewing angles between 0 degrees and 40degrees with respect to the normal to the surface of the fourth exampleof the optical structure 300 a/300 b. As the viewing angle increases thecolor of the fourth example of the optical structure 300 a/300 b in thetransmission mode shifts in the direction of the arrow 1803. The colorof the fourth example in the transmission mode can have a lightness (L*)value between approximately 27.1 and approximately 62.1 for differentviewing angles between 0 degrees and 40 degrees with respect to thenormal to the surface of the fourth example of the optical structure 300a/300 b. The color of the fourth example in the transmission mode canhave an (a*) value between approximately 20.5 and approximately 47.2 fordifferent viewing angles between 0 degrees and 40 degrees with respectto the normal to the surface of the fourth example of the opticalstructure 300 a/300 b. The color of the fourth example in thetransmission mode can have a (b*) value between approximately 29.5 andapproximately 74.3 for different viewing angles between 0 degrees and 40degrees with respect to the normal to the surface of the fourth exampleof the optical structure 300 a/300 b.

FIG. 28E is a CIE 1931 color space chromaticity diagram showing the xand y chromaticity coordinates of light reflected from the fourthexample of the optical structure 300 a or 300 b for different viewingangles between 0 degrees and 40 degrees with respect to a normal to asurface of the optical structure 300 a or 300 b. As the viewing angleincreases, the color of the optical structure 300 a or 300 b changesfrom yellow-green towards aquamarine in the direction of the arrow 1805.FIG. 28F illustrates the a*b* values in the CIE L*a*b* color space whenthe fourth example of the optical structure 300 a/300 b is viewed in thereflection mode at different viewing angles between 0 degrees and 40degrees with respect to the normal to the surface of the fourth exampleof the optical structure 300 a/300 b. As the viewing angle increases thecolor of the fourth example of the optical structure 300 a/300 b in thereflection mode shifts in the direction of the arrow 1807. The color ofthe fourth example in the reflection mode can have a lightness (L*)value between approximately 53.3 and approximately 88.5 for differentviewing angles between 0 degrees and 40 degrees with respect to thenormal to the surface of the fourth example of the optical structure 300a/300 b. The color of the fourth example in the reflection mode can havean (a*) value between approximately −13.9 and approximately −65.5 fordifferent viewing angles between 0 degrees and 40 degrees with respectto the normal to the surface of the fourth example of the opticalstructure 300 a/300 b. The color of the fourth example in the reflectionmode can have a (b*) value between approximately −13.0 and approximately59.9 for different viewing angles between 0 degrees and 40 degrees withrespect to the normal to the surface of the fourth example of theoptical structure 300 a/300 b.

FIG. 29A shows the variation of the transmittance, reflectance andabsorptance with wavelength for a fifth example of the optical structure300 a/300 b at a viewing angle of 0 degrees with respect to a normal tothe surface of the optical structure 300 a/300 b. In FIG. 29A, curve1901 shows the variation of transmittance with wavelength, curve 1903shows the variation of reflectance with wavelength, and curve 1905 showsthe variation of absorptance with wavelength. The fifth example of theoptical structure 300 a or 300 b comprises a layer of gold (Au)(corresponding to the layer 301 b of FIG. 24A or the region 310 of FIG.24B) having a thickness of about 40 nm surrounded by two layers of adielectric material comprising zinc sulfide (ZnS) (corresponding to thelayers 303 a and 303 b of FIG. 24A or the region 312 of FIG. 24B) havingan individual thickness of about 80 nm. The fifth example furthercomprises two additional gold layers disposed over the two dielectriclayers (corresponding to the layers 301 a and 301 c of FIG. 24A or theregion 314 of FIG. 24B) having an individual thickness of about 23 nm.The fifth example of the optical structure 300 a or 300 b isencapsulated in a SiO₂ matrix which is used to simulate the printingmedium or ink which has a similar refractive index.

It is observed from FIG. 29A that the transmittance through the fifthexample of the optical structure 300 a/300 b is greater than about 10%for wavelengths greater than about 550 nm and less than about 700 nm.The maximum value of the transmittance occurs at a wavelength betweenabout 600 nm and about 650 nm. It is further observed from FIG. 29A thatthe reflectance from the fifth example of the optical structure 300a/300 b is greater than 30% for wavelengths between about 430 nm andabout 580 nm. The fifth example of the optical structure 300 a/300 b hassignificant absorptance (e.g., greater than about 10%) for wavelengthsbetween about 400 nm and about 700 nm. Accordingly, the color in thetransmission mode is not expected to be complementary to the color inthe reflection mode.

FIG. 29B is a CIE 1931 color space chromaticity diagram showing the xand y chromaticity coordinates of light transmitted through the fifthexample of the optical structure 300 a or 300 b for different viewingangles between 0 degrees and 40 degrees with respect to a normal to asurface of the optical structure 300 a or 300 b. FIG. 29C illustratesthe a*b* values in the CIE L*a*b* color space when the fifth example ofthe optical structure 300 a/300 b is viewed in the transmission mode atdifferent viewing angles between 0 degrees and 40 degrees with respectto the normal to the surface of the fifth example of the opticalstructure 300 a/300 b. As the viewing angle increases the color of thefourth example of the optical structure 300 a/300 b in the transmissionmode shifts in the direction of the arrow 1907. The color of the fifthexample in the transmission mode can have a lightness (L*) value betweenapproximately 54.0 and approximately 58.5 for different viewing anglesbetween 0 degrees and 40 degrees with respect to the normal to thesurface of the fifth example of the optical structure 300 a/300 b. Thecolor of the fifth example in the transmission mode can have an (a*)value between approximately 35.0 and approximately 40.3 for differentviewing angles between 0 degrees and 40 degrees with respect to thenormal to the surface of the fifth example of the optical structure 300a/300 b. The color of the fifth example in the transmission mode canhave a (b*) value between approximately 62.8 and approximately 74.9 fordifferent viewing angles between 0 degrees and 40 degrees with respectto the normal to the surface of the fifth example of the opticalstructure 300 a/300 b.

FIG. 29D is a CIE 1931 color space chromaticity diagram showing the xand y chromaticity coordinates of light reflected from the fifth exampleof the optical structure 300 a or 300 b for different viewing anglesbetween 0 degrees and 40 degrees with respect to a normal to a surfaceof the optical structure 300 a or 300 b. FIG. 29E illustrates the a*b*values in the CIE L*a*b* color space when the fifth example of theoptical structure 300 a/300 b is viewed in the reflection mode atdifferent viewing angles between 0 degrees and 40 degrees with respectto the normal to the surface of the fifth example of the opticalstructure 300 a/300 b. As the viewing angle increases the color of thefifth example of the optical structure 300 a/300 b in the reflectionmode shifts in the direction of the arrow 1909. The color of the fifthexample in the reflection mode can have a lightness (L*) value betweenapproximately 64.5 and approximately 77.3 for different viewing anglesbetween 0 degrees and 40 degrees with respect to the normal to thesurface of the fifth example of the optical structure 300 a/300 b. Thecolor of the fifth example in the reflection mode can have an (a*) valuebetween approximately −60.1 and approximately −63.7 for differentviewing angles between 0 degrees and 40 degrees with respect to thenormal to the surface of the fifth example of the optical structure 300a/300 b. The color of the fifth example in the reflection mode can havea (b*) value between approximately −0.1 and approximately 6.6 fordifferent viewing angles between 0 degrees and 40 degrees with respectto the normal to the surface of the fifth example of the opticalstructure 300 a/300 b.

Without relying on any particular theory, the color in the reflectionand the transmission mode is dependent on the thickness and thecomposition of the different layers of the optical structure 300 a or300 b. For example, in some implementations little to no light istransmitted through an implementation of an optical structure 300 a or300 b in which the dielectric layers 303 a and 303 b are absent. Thebrightness of the color in the reflection mode can increase as thethickness of the metal layers 301 a, 301 b, and 301 c increases whilethe brightness of the color in the transmission mode can decrease as thethickness of the metal layers 301 a, 301 b, and 301 c increases incertain implementations.

Without subscribing on any particular theory, various implementations ofthe optical structure 300 a or 300 b can exhibit variation in thereflected and/or transmitted color as the viewing angle changes. Thevariation in the reflected and/or transmitted color with change in theviewing angle can be large (or significant) if the refractive index ofthe dielectric material of the layers 303 a and 303 b has a refractiveindex less than about 2.0. For example, the variation in the reflectedand/or transmitted color with change in the viewing angle can be large(or significant) if the layers 303 a and 303 b comprises silica (SiO₂)having a refractive index of about 1.5 or magnesium fluoride (MgF₂)having a refractive index of about 1.39. The variation in the reflectedand/or transmitted color with change in the viewing angle can be small(or insignificant) if the refractive index of the dielectric material ofthe layers 303 a and 303 b has a refractive index greater than about2.0. For example, the variation in the reflected and/or transmittedcolor with change in the viewing angle can be small (or insignificant)if the layers 303 a and 303 b comprises zinc sulfide (ZnS) having arefractive index of about 2.38 or other high refractive index materialssuch as, for example, zirconium dioxide (ZrO₂) or ceric oxide (CeO₂). Invarious implementations, the variation in the reflected and/ortransmitted color with change in the viewing angle can depend on thethickness of the dielectric layers 303 a and 303 b.

The optical structures 300 a/300 b configured as foil, film or plateletscan be incorporated with or in a document (e.g., a banknote), package,product, or other item. Optical products such as a film, a thread, alaminate, a foil, a pigment, or an ink comprising one or more of theoptical structures 300 a/300 b discussed above can be incorporated withor in documents such as banknotes or other documents to verifyauthenticity of the documents, packaging materials, etc. For example,the optical structures 300 a/300 b can be configured as an ink or apigment which is disposed on a base comprising at least one of apolymer, a plastic, a paper or a fabric. The base may be flexible insome implementations. The base comprising the ink or a pigment orpigment comprising the optical structures 300 a or 300 b can be cut ordiced to obtain a thread or a foil. A plurality of optical structures300 a or 300 b discussed above can be incorporated in a particularoptical product (e.g., ink, pigment, thread, filament, paper, securityink, security pigment, security thread, security filament, securitypaper, etc.). The shapes, sizes and/or aspect ratios of the plurality ofoptical structures 300 a or 300 b discussed above that are incorporatedin a particular optical product (e.g., ink, pigment, thread, filament,paper, security ink, security pigment, security thread, securityfilament, security paper, etc.) can vary. Accordingly, a particularoptical product (e.g., ink, pigment, thread, filament, paper, securityink, security pigment, security thread, security filament, securitypaper, etc.) can comprise optical structures 300 a or 300 b withdifferent distributions of shapes, sizes and/or aspect ratios of theoptical structures. For example, a particular optical product (e.g.,ink, pigment, thread, filament, paper, security ink, security pigment,security thread, security filament, security paper, etc.) can compriseoptical structures 300 a or 300 b with sizes distributed around one ormore mean sizes. As another example, a particular optical product (e.g.,ink, pigment, thread, filament, paper, security ink, security pigment,security thread, security filament, security paper, etc.) can compriseoptical structures 300 a or 300 b with aspect ratios distributed aroundone or more aspect ratios.

As discussed above, the color in the reflection mode and thetransmission mode of an implementation of an optical structure 300 a or300 b depends on the thickness and the composition of the various metallayers and the various dielectric layers that form the implementation ofthe optical structure 300 a or 300 b. Accordingly, the reflected and/ortransmitted color of a particular optical product (e.g., ink, pigment,thread, filament, paper, security ink, security pigment, securitythread, security filament, security paper, etc.) can be tailored byincorporated plurality of optical structures 300 a or 300 b havingdifferent thicknesses and/or compositions of the various constituentlayers. By combining plurality of optical structures 300 a or 300 bhaving different thicknesses and/or compositions of the variousconstituent layers, optical products (e.g., ink, pigment, thread,filament, paper, security ink, security pigment, security thread,security filament, security paper, etc.) having different reflectedand/or transmitted colors can be manufactured.

FIGS. 30A and 30B are CIE 1931 color space chromaticity diagramsrespectively showing the x and y chromaticity coordinates of lighttransmitted through and reflected from various implementations of anoptical structure having a geometry similar to optical structure 300 aor 300 b. The various implementations of the optical structure includethree metal layers comprising silver (Ag) and two dielectric layerscomprising zinc sulfide (ZnS). The thickness of a central metal layercomprising silver (Ag) (e.g., corresponding to layer 301 b in FIG. 24Aor region 310 in FIG. 24B) can be about 40 nm in the variousimplementations of the optical structure. The thickness of thesurrounding metal layers comprising silver (Ag) (e.g., corresponding tolayers 301 a and 301 c in FIG. 24A or region 314 in FIG. 24B) can beabout 25 nm in the various implementations of the optical structure. Thethickness of the two dielectric layers (e.g., corresponding to layers303 a and 303 b in FIG. 24A or region 312 in FIG. 24B) can be in a rangebetween about 40 nm and about 183 nm in the various implementations ofthe optical structure.

For example, the region 2001 in FIG. 30A shows the x and y chromaticitycoordinates of light transmitted through an implementation of an opticalstructure with two dielectric layers comprising zinc sulfide (ZnS)having an individual thickness of about 95 nm. The region 2003 in FIG.30B shows the corresponding x and y chromaticity coordinates of lightreflected from the implementation of the optical structure with twodielectric layers comprising zinc sulfide (ZnS) having an individualthickness of about 95 nm. As another example, the region 2005 in FIG.30A shows the x and y chromaticity coordinates of light transmittedthrough an implementation of an optical structure with two dielectriclayers comprising zinc sulfide (ZnS) having an individual thickness ofabout 66 nm. The region 2007 in FIG. 30B shows the corresponding x and ychromaticity coordinates of light reflected from the implementation ofthe optical structure with two dielectric layers comprising zinc sulfide(ZnS) having an individual thickness of about 66 nm.

As noted from FIGS. 30A and 30B implementations of optical structureswith different thickness of the dielectric layers produce differentcolors in the transmission and reflection mode. For example, otherregions corresponding to other designs are also shown in the CIE 1931color space chromaticity diagrams of FIGS. 30A and 30B. Accordingly,pigments and/or inks that are configured to produce a wide variety ofcolors in a color space can be obtained by varying the thickness of theindividual dielectric layers of the constituent optical structures.Other variations, for example, of the material composition and/orthickness of the other layers (metal and/or dielectric) are possible.Such different designs may provide different colors and/or othercharacteristics such as amount of color shift with angle, etc.

The optical performance of example optical structures with and withoutprotective dielectric layers having parameters provided in Tables 9 and10 were analyzed. The material composition and the thickness of thevarious layers for the example optical structure without protectivelayers are provided in Table 9 and the material composition and thethickness of the various layers for the example optical structure withprotective layers are provided in Table 10.

TABLE 9 Material Composition and thickness of the various layers of anexample optical structure without protective layers. Optical PhysicalThickness (Full Wavelength Refractive Extinction Optical Thickness LayerMaterial Index Coefficient Thickness) (nm) SiO2 1.46180 0.00000 1 Ag0.05100 2.96000 0.00250000 25.00 2 ZnS 2.37920 0.00000 0.30789645 66.003 Ag 0.05100 2.96000 0.00400000 40.00 4 ZnS 2.37920 0.00000 0.3078964566.00 5 Ag 0.05100 2.96000 0.00250000 25.00 Substrate Glass 1.520830.00000

TABLE 10 Material Composition and thickness of the various layers of anexample optical structure with protective layers. Optical PhysicalThickness (Full Wavelength Refractive Extinction Optical ThicknessMedium Index Coefficient Thickness) (nm) SiO2 1.46180 0.00000 1 ZnS2.37920 0.00000 0.04665098 10.00 2 Ag 0.05100 2.96000 0.00250000 25.00 3ZnS 2.37920 0.00000 0.30789645 66.00 4 Ag 0.05100 2.96000 0.0040000040.00 5 ZnS 2.37920 0.00000 0.30789645 66.00 6 Ag 0.05100 2.960000.00250000 25.00 7 ZnS 2.37920 0.00000 0.04665098 10.00 Substrate Glass1.52083 0.00000

The material composition of the various layers of the example opticalstructure with protective layers is the same as the material compositionof the various layers of the example optical structure withoutprotective layers but with the additional protective layers. Forexample, the example optical structures comprise an Ag layer having athickness of 40 nm sandwiched by two ZnS layers each having a thicknessof 66 nm. Two Ag layers each having a thickness of 25 nm are disposed onthe side of the two ZnS layers opposite the side facing the Ag layerhaving a 40 nm thickness. The example optical structure with theprotective layers included additional ZnS layers each having a thicknessof 10 nm. The SiO₂ layer and glass layer represent the medium (e.g.,refractive indices of approximately 1.4-1.6) in which the optical stackis immersed (e.g., organic vehicle for pigment). In both examples, whenoutputting a spectral scan, SiO₂ and glass can index match the organicvehicle and in effect disappear with respect to the optical performanceof the optical stack.

Table 11 provides the CIELa*b* values for transmission mode when theexample optical structure without protective layers (e.g., havingparameters as described in Table 9) is viewed at different viewingangles in the presence of a D65 light source. Table 12 provides theCIELa*b* values for transmission mode when the example optical structurewith protective layers (e.g., having parameters as described in Table10) is viewed at different viewing angles in the presence of a D65 lightsource.

TABLE 11 CIELab values for transmission mode when the example opticalstructure without protective layers (e.g., having parameters asdescribed in Table 9) is viewed at different viewing angles in thepresence of a D65 light source. Design ZnS with 3 layers of Ag dichroicdesign Polarisation P Source D65 Observer CIE 1931 Mode TransmittanceIncident Angle L* a* b* Wht Pt 100.0000 0.0000 0.0000 0.0 75.0871−72.4036 71.2058 5.0 75.0948 −72.6351 71.1003 10.0 75.1162 −73.325170.7800 15.0 75.1464 −74.4601 70.2335 20.0 75.1770 −76.0180 69.4423 25.075.1956 −77.9679 68.3802 30.0 75.1849 −80.2708 67.0130 35.0 75.1217−82.8794 65.2976 40.0 74.9748 −85.7385 63.1796

TABLE 12 CIELab values for transmission mode when the example opticalstructure with protective layers (e.g., having parameters as describedin Table 10) is viewed at different viewing angles in the presence of aD65 light source. Design ZnS with 3 layers of Ag dichroic designPolarisation P Source D65 Observer CIE 1931 Mode Transmittance IncidentAngle L* a* b* Wht Pt 100.0000 0.0000 0.0000 0.0 78.6293 −69.641369.0996 5.0 78.6168 −69.9121 69.0059 10.0 78.5767 −70.7180 68.7193 15.078.5019 −72.0398 68.2237 20.0 78.3805 −73.8464 67.4936 25.0 78.1956−76.0948 66.4964 30.0 77.9258 −78.7316 65.1949 35.0 77.5441 −81.693463.5499 40.0 77.0167 −84.9067 61.5232

FIGS. 31A and 31B respectively illustrate the transmittance andreflectance spectra for the example optical structures with and withoutprotective layers. With additional protective layers, the color intransmission or reflection (e.g., as indicated by the peaks and dips) isnot greatly impacted. Hence, in various implementations, protectivelayers can be used to enhance durability, allow for safer processing,reduce oxidation and/or corrosion with negligible effect on opticalperformance in transmission and/or reflection.

The disclosure set forth herein describes a wide variety of structuresand methods but should not be considered to be limited to thoseparticular structures or methods. For example, although many of theexample optical structures 10, 300 a, or 300 b are symmetrical,asymmetric structures are also possible. For example, instead of havinga pair of similar or identical dielectric layers sandwiching the pair ofmetallic layers, either dielectric or metal layers having differentcharacteristics (e.g., thickness or material) may be used on oppositesides of the structure or alternatively, maybe only one side of the pairof metal layers has a dielectric layer thereon. Similarly, the metallayers need not be identical and may have different characteristics suchas different thicknesses or materials. As described above, interveninglayers may also be included. One or more such intervening layer may beinclude such that the optical structure is not symmetric. For example,one or more intervening layers may be included between the dielectriclayer 12 and metal layer 13 (or the dielectric layer 303 a and the metallayer 301 a) and not between that metal layer 15 and the dielectriclayer 16 (or the dielectric layer 303 b and the metal layer 301 c) orvice versa. Similarly, one or more intervening layers may be includedbetween the metal layer 13 and the dielectric layer 14 and not betweenthe dielectric layer 14 and the metal layer 15, or vice versa. Likewise,one or more intervening layers having different characteristics (e.g.,material or thickness) may be included on different sides of the opticalstructure 10, 300 a, or 300 b. Or more intervening layers may beincluded on one side of the optical structure 10, 300 a or 300 b than onthe other side of the optical structure. For example, the metal layer13, the metal layer 15, the metal layer 301 a, the metal layer 301 band/or the metal layer 301 c can comprise metal sub-layers. In someimplementations, the metal layer 13 and/or the metal layer 15 cancomprise a first metal (e.g., silver) facing the high refractive indextransparent layers 12 or 16 and a second metal (e.g., gold) facing thedielectric layer 14. In some implementations, the metal layer 301 a andthe metal layer 301 c can comprise a first metal (e.g., gold) and themetal layer 301 b can comprise a second metal (e.g., silver). Othervariations are possible.

Likewise, although this disclosure describes applications of thestructures and method describe herein to include security applications,e.g., countering successful use of counterfeit currency, documents, andproducts, this disclosure should not be considered to be limited tothose particular applications. Alternatively or in addition, suchfeatures could, for example, be used for providing an aesthetic effect,to create appealing or attractive features on products or packaging formarketing and advertisement, or for other reasons.

Dimensions, such as, thickness, length, width of various embodimentsdescribed herein can be outside the different ranges provided in thisdisclosure. The values of refractive indices for the various materialsdiscussed herein can be outside the different ranges provided in thisdisclosure. The values for reflectance and/or transmittance of thedifferent structures can be outside the different ranges providedherein. The values for spectral widths and peak locations for thereflection and transmission spectra can be outside the different rangesprovided herein.

The entirety of each application below is incorporated herein byreference: U.S. patent application Ser. No. 14/921,933 (Attorney DocketNo. WVFRNT.011A) filed on Oct. 23, 2015, which claims the benefit ofpriority of U.S. Provisional Application No. 62/068,540 (Attorney DocketNo. WVFRNT.011PR) filed on Oct. 24, 2014; U.S. patent application Ser.No. 16/054,898 (Attorney Docket No. WVFRNT.017A) filed on Aug. 3, 2018,which claims the benefit of priority of U.S. Provisional Application No.62/568,711 (Attorney Docket No. WVFRNT.017PR) filed on Oct. 5, 2017; andU.S. patent application Ser. No. 16/780,777 (Attorney Docket No.WVFRNT.019A) filed on Feb. 3, 2020, which claims the benefit of priorityof U.S. Provisional Application No. 62/829,572 (Attorney Docket No.WVFRNT.019PR) filed on Apr. 4, 2019.

Examples

The following is a numbered list of example embodiments that are withinthe scope of this disclosure. The example embodiments that are listedshould in no way be interpreted as limiting the scope of theembodiments. Various features of the example embodiments that are listedcan be removed, added, or combined to form additional embodiments, whichare part of this disclosure. 1. An optical product configured, whenilluminated, to reproduce an image that appears 3D of at least a part ofa 3D object, said optical product comprising:

-   -   a surface comprising a plurality of portions, each portion        corresponding to a point on a surface of said 3D object;    -   one or more non-holographic features disposed within each        portion configured to produce at least part of said image        without relying on diffraction;    -   an interference optical structure disposed with respect to said        one or more non-holographic features;    -   wherein for individual ones of the portions, a gradient in said        non-holographic features correlates to a surface normal of said        surface of said 3D object at said corresponding point, and    -   wherein for individual ones of the portions, an orientation of        said non-holographic features correlates to an orientation of        said surface of said 3D object at said corresponding point.

2. The optical product of Example 1, when illuminated, reproduces theimage in a first color in transmission mode or a second color inreflection mode.

3. The optical product of any of Examples 1-2, when illuminated,reproduces the image in a first color in transmission mode and a secondcolor in reflection mode, wherein the second color is different from thefirst color.

4. The optical product of any of Examples 1-3, wherein the first colorand/or the second color changes with a change in a viewing angle.

5. The optical product of any of Example 1-3, wherein the first colorand/or the second color does not change with a change in a viewingangle.

6. The optical product of any of Examples 1-5, wherein said opticalstructure comprises an interference optical stack.

7. The optical product of any of Examples 1-6, wherein said opticalstructure comprises a D/M/D/M/D multilayer thin film optical stack,where D is a transparent or optically transmissive dielectric layer andM is a metal layer.

8. The optical product of Example 7, wherein the metal layers have aratio of the real part (n) of the refractive index to the imaginary part(k) of the refractive index greater than or equal to 0.01 and less thanor equal to 0.5.

9. The optical product of any of Examples 1-6, wherein said opticalstructure comprises a M/D/M/D/M multilayer thin film optical stack,where D is a transparent or optically transmissive dielectric layer andM is a metal layer.

10. The optical product of Example 9, wherein the metal layers have aratio of the real part (n) of the refractive index to the imaginary part(k) of the refractive index greater than or equal to 0.01 and less thanor equal to 0.2.

11. The optical product of any of Examples 9-10, wherein individual onesof the metal layers have a thickness from about 20 nm to about 100 nm.

12. The optical product of any of Examples 7-11, wherein at least one ofthe metal layers comprises aluminum, silver, gold, silver alloy, or goldalloy.

13. The optical product of any of Examples 7-12, wherein at least one ofthe dielectric layers comprises magnesium fluoride, silicon dioxide,zinc oxide, zinc sulfide, zirconium dioxide, titanium dioxide, tantalumpentoxide, ceric oxide, yttrium oxide, indium oxide, tin oxide, indiumtin oxide, aluminum oxide, tungsten trioxide, or combinations thereof.

14. The optical product of any of Examples 7-12, wherein at least one ofthe dielectric layers comprises an organic layer.

15. The optical product of any of Examples 1-6, wherein said opticalstructure comprises a H/L/H/L/H multilayer thin film optical stack,wherein H and L are layers with a refractive index, and wherein the Hlayers have a higher refractive index than the L layers.

16. The optical product of Example 15, wherein the L layers have arefractive index less than 1.65 and the H layers have a refractive indexgreater than or equal to 1.65.

17. The optical product of any of Examples 1-6, wherein said opticalstructure comprises a A/D/M multilayer thin film optical stack, where Ais an absorber layer, D is a transparent dielectric layer, and M is ametal layer that is opaque.

18. The optical product of Example 17, wherein the metal layer has aratio of the real part (n) of the refractive index to the imaginary part(k) of the refractive index near unity.

19. The optical product of any of Examples 17-18, wherein said opticalstructure comprises a A/D/M/D/A multilayer thin film optical stack.

20. The optical product of any of Examples 17-19, wherein said opticalstructure comprises a A/D/M/M*/M/D/A multilayer thin film optical stack,where M* is a magnetic layer.

21. The optical product of any of Examples 1-6, wherein said opticalstructure comprises a Fabry-Perot or etalon structure.

22. The optical product of any of the preceding examples, wherein saidnon-holographic features comprise facets.

23. The optical product of any of the preceding examples, wherein saidnon-holographic features comprise linear or curved facets.

24. The optical product of any of the preceding examples, wherein saidnon-holographic features with less steep slopes are configured toreflect light toward an observer's eye, and wherein said non-holographicfeatures with steeper slopes are configured to reflect light away fromthe observer's eye.

25. The optical product of any of the preceding examples, wherein saidportions comprise non-holographic features with discontinuitiescorresponding to a continuous region of said 3D object.

26. The optical product of any of the preceding examples, wherein said3D object comprises an irregularly shaped object.

27. The optical product of any of the preceding examples, wherein theoptical structure is in the form of a hot stamp coating, a foil coating,or an ink coating.

28. The optical product of any of the preceding examples, wherein theoptical product is in the form of a thread, patch, laminate, hot stamp,or window.

29. The optical product of any of the preceding examples, wherein saidoptical product is configured to provide authenticity verification on anitem for anti-counterfeiting or security.

30. The optical product of Example 29, wherein said item is a banknote,a credit card, a debit card, a passport, a driver's license, anidentification card, a document, a tamper evident container orpackaging, or a bottle of pharmaceuticals.

31. The optical product of Example 29, wherein said item is electronics,apparel, jewelry, cosmetics, or a handbag.

32. The optical product of any of the preceding examples, wherein aninclination of said surface of said 3D object comprises a polar anglefrom a first reference line of said 3D object, and wherein saidorientation of said surface of said 3D object comprises an azimuth anglefrom a second reference line orthogonal to said first reference line ofsaid 3D object.

33. The optical product of any of the preceding examples, wherein saidimage is a substantially similar reproduction of said 3D object and notscaled up in size.

34. The optical product of any of the preceding examples, wherein saidnon-holographic features form a shape different from said 3D object.

35. The optical product of any of the preceding examples, wherein amajority of said plurality of portions comprises non-holographicfeatures with discontinuities.

36. The optical product of any of the preceding examples, wherein saidportions of said plurality of portions are defined by borders.

37. The optical product of any of the preceding examples, wherein saidportions of said plurality of portions are defined by linear borders.

38. The optical product of any of the preceding examples, wherein amajority of said plurality of portions comprises features discontinuouswith features in surrounding adjacent portions.

39. The optical product of any of the preceding examples, wherein amajority of said non-holographic features is discontinuous at linearboundaries between adjacent portions.

40. The optical product of any of the preceding examples, wherein saidplurality of portions comprises non-holographic features withdiscontinuities corresponding to a continuous region of said 3D object.

41. The optical product of any of the preceding examples, furthercomprising holographic features.

42. The optical product of any of the previous examples, whereinportions of the plurality of portions have a length and width between 10μm and 55 μm.

43. The optical product of any of the preceding examples, whereinportions of the plurality of portions have a length and width between 20μm and 50 μm.

44. The optical product of any of the preceding examples, wherein theoptical product comprises a first surface and a second surface oppositesaid first surface, wherein said plurality of portions are disposed onthe second surface, wherein the non-holographic features comprise one ormore non-linear features when viewed in a cross-section orthogonal tosaid first and second surfaces.

45. The optical product of any of the preceding examples, wherein said3D object comprises a non-symmetrical shaped object.

46. The optical product of any of the preceding examples, wherein said3D object comprises an object in nature.

47. The optical product of any of the preceding examples, wherein said3D object comprises a man-made object.

48. The optical product of any of the preceding examples, wherein thenon-holographic features are configured to produce at least part of theimage without lenses.

49. The optical product of any of the preceding examples, wherein theoptical product comprises a first surface and a second surface oppositesaid first surface, wherein said plurality of portions are disposed onsaid second surface, and wherein said first surface is planar.

50. The optical product of any of Examples 1-6, wherein said opticalstructure comprises a M/D/M multilayer thin film optical stack, where Dis a transparent or optically transmissive dielectric layer and M is ametal layer.

51. The optical product of any of Examples 1-6, wherein said opticalstructure comprises a D/M/D multilayer thin film optical stack, where Dis a transparent or optically transmissive dielectric layer and M is ametal layer.

Various embodiments of the present invention have been described herein.Although this invention has been described with reference to thesespecific embodiments, the descriptions are intended to be illustrativeof the invention and are not intended to be limiting. Variousmodifications and applications may occur to those skilled in the artwithout departing from the true spirit and scope of the invention.

1. An optical product configured, when illuminated, to reproduce animage that appears 3D of at least a part of a 3D object, said opticalproduct comprising: a surface comprising a plurality of portions, eachportion corresponding to a point on a surface of said 3D object; one ormore non-holographic features disposed within each portion configured toproduce at least part of said image without relying on diffraction; aninterference optical structure disposed with respect to said one or morenon-holographic features; wherein for individual ones of the portions, agradient in said non-holographic features correlates to a surface normalof said surface of said 3D object at said corresponding point, andwherein for individual ones of the portions, an orientation of saidnon-holographic features correlates to an orientation of said surface ofsaid 3D object at said corresponding point.
 2. (canceled)
 3. The opticalproduct of claim 1, when illuminated, reproduces the image in a firstcolor in transmission mode and a second color in reflection mode,wherein the second color is different from the first color. 4.(canceled)
 5. (canceled)
 6. The optical product of claim 1, wherein saidinterference optical structure comprises an interference optical stack.7.-21. (canceled)
 22. The optical product of claim 1, wherein saidnon-holographic features comprise facets.
 23. The optical product ofclaim 1, wherein said non-holographic features comprise linear or curvedfacets.
 24. The optical product of claim 1, wherein said non-holographicfeatures with less steep slopes are configured to reflect light towardan observer's eye, and wherein said non-holographic features withsteeper slopes are configured to reflect light away from the observer'seye.
 25. (canceled)
 26. (canceled)
 27. The optical product of claim 1,wherein the interference optical structure is in the form of a hot stampcoating, a foil coating, or an ink coating.
 28. The optical product ofclaim 1, wherein the optical product is in the form of a thread, patch,laminate, hot stamp, or window.
 29. The optical product of claim 1,wherein said optical product is configured to provide authenticityverification on an item for anti-counterfeiting or security.
 30. Theoptical product of claim 29, wherein said item is a banknote, a creditcard, a debit card, a stock certificate, a passport, a driver's license,an identification card, a document, a tamper evident container orpackaging, consumer packaging, or a bottle of pharmaceuticals.
 31. Theoptical product of claim 29, wherein said item is electronics, apparel,jewelry, cosmetics, or a handbag.
 32. The optical product of claim 1,wherein said image is a substantially similar reproduction of said 3Dobject and not scaled up in size.
 33. The optical product of claim 1,wherein said non-holographic features form a shape different from said3D object.
 34. The optical product of claim 1, wherein the opticalproduct comprises a first surface and a second surface opposite saidfirst surface, wherein said plurality of portions are disposed on thesecond surface, wherein the non-holographic features comprise one ormore non-linear features when viewed in a cross-section orthogonal tosaid first and second surfaces.
 35. The optical product of claim 1,wherein the non-holographic features are configured to produce at leastpart of the image without lenses.